JCP Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

You Tube Flickr Twitter iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue

15 Dec 1991

Volume 95, Issue 12, pp. 8693-9433

Page 1 of 4 Pages Next Page | Jump to Page

Raman study on molecular motion in tetramethylammonium hydroxide pentahydrate

Isao Kanesaka, Makoto Iwaki, Chikayo Uezawa, Nobuhiro Kuriyama, Tetsuo Sakai, Hiroshi Miyamura, and Hiroshi Ishikawa

J. Chem. Phys. 95, 8693 (1991); http://dx.doi.org/10.1063/1.461254 (4 pages) | Cited 2 times

Full Text: | Download PDF

Show Abstract
The Raman spectrum as well as conductivity and differential‐thermal‐analysis (DTA) thermogram of tetramethylammonium hydroxide pentahydrate was observed at various temperatures in order to investigate molecular motion in relation to conductivity and a phase transition. It was clarified that different stepwise protonation processes become effective for relaxation in the O–H stretching of hydroxide ions as temperature is increased. The activation energy was 6.1 and 16.0 kJ/mol in 130≤T<210 and 210≤T≤250 K, respectively, whereas the activation energy in conductivity was 41.1 kJ/mol below 250 K. This discrepancy was discussed according to a reorientational motion of water molecules. The Raman band shape of the NM4 asymmetric stretching of tetramethylammonium ions was analyzed on the basis of the reorientational motion about the C3 and C2 axes on the ion, and the activation energies were 8.7 kJ/mol (about the C3 axis) and 14.5 kJ/mol (about the C2 axis).
Show PACS
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
78.30.Jw Organic compounds, polymers
72.80.-r Conductivity of specific materials
33.20.Tp Vibrational analysis

Reactions of boron atoms with molecular oxygen. Infrared spectra of BO, BO2, B2O2, B2O3, and BO−2 in solid argon

Thomas R. Burkholder and Lester Andrews

J. Chem. Phys. 95, 8697 (1991); http://dx.doi.org/10.1063/1.461814 (13 pages) | Cited 88 times

Full Text: | Download PDF

Show Abstract
Boron atoms from Nd:YAG laser ablation of the solid have been codeposited with Ar/O2 samples on a 11±1 K salt window. The product infrared spectrum was dominated by three strong 11B isotopic bands at 1299.3, 1282.8, and 1274.6 cm−1 with 10B counterparts at 1347.6, 1330.7, and 1322.2 cm−1. Oxygen isotopic substitution (16O18O and 18O2 ) confirms the assignment of these strong bands to ν3 of linear BO2. Renner–Teller coupling is evident in the ν2 bending motion. A sharp medium intensity band at 1854.7 has appropriate isotopic ratios for BO, which exhibits a 1862.1 cm−1 gas phase fundamental. A sharp 1931.0 cm−1 band shows isotopic ratios appropriate for another linear BO2 species; correlation with spectra of BO−2 in alkali halide lattices confirms this assignment. A weak 1898.9 cm−1 band grows on annealing and shows isotopic ratios for a BO stretching mode and isotopic splittings for two equivalent B and O atoms, which confirms assignment to B2O2. A weak 2062 cm−1 band grows markedly on annealing and shows isotope shifts appropriate for a terminal–BO group interacting with another oxygen atom; the 2062 cm−1 band is assigned to B2O3 in agreement with earlier work. A strong 1512.3 cm−1 band appeared on annealing; its proximity to the O2 fundamental at 1552 cm−1 and pure oxygen isotopic shift suggest that this absorption is due to a B atom–O2 complex.
Show PACS
33.20.Ea Infrared spectra
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

Intersystem crossing dynamics in Fe(II) coordination compounds

Andreas Hauser, Andreas Vef, and Peter Adler

J. Chem. Phys. 95, 8710 (1991); http://dx.doi.org/10.1063/1.461255 (8 pages) | Cited 45 times

Full Text: | Download PDF

Show Abstract
The 5T2(HS)→1A1(LS) intersystem crossing rates have been determined for a number of Fe(II) coordination compounds between 10 and 270 K using time‐dependent optical spectroscopy. Strong deviations from Arrhenius kinetics with nearly temperature independent tunneling at low temperatures and a thermally activated behavior at elevated temperatures with apparent activation energies smaller than the classical energy barrier were found. The tunneling rates range from ∼10−6 s−1 for the doped spin crossover system [Zn1−xFex(ptz)6](BF4)2 to ∼106 s−1 for the doped low‐spin (LS) system [Zn1−xFex(bipy)3](PF6)2. The large range of 12 orders of magnitude in the low temperature tunneling rates as well as the activated region can be understood in terms of nonadiabatic multiphonon relaxation. Values for the Huang–Rhys parameter S of 40–50 and for the reduced energy gap p of 1–12 are estimated for the present series of compounds. The validity of an inverse energy gap law in the strong vibronic coupling limit with S≫p is borne out by experiment.
Show PACS
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
31.50.Df Potential energy surfaces for excited electronic states

Rotationally resolved photoelectron spectra in resonance enhanced multiphoton ionization of HCl via the F 1Δ2 Rydberg state

Kwanghsi Wang and V. McKoy

J. Chem. Phys. 95, 8718 (1991); http://dx.doi.org/10.1063/1.461256 (7 pages) | Cited 16 times

Full Text: | Download PDF

Show Abstract
Results of studies of rotational ion distributions in the X 2Π3/2 and X 2Π1/2 spin‐orbit states of HCl+ resulting from (2+1′) resonance enhanced multiphoton ionization (REMPI) via the S(0) branch of the F 1Δ2 Rydberg state are reported and compared with measured threshold‐field‐ionization zero‐kinetic‐energy spectra reported recently [K. S. Haber, Y. Jiang, G. Bryant, H. Lefebvre‐Brion, and E. R. Grant, Phys. Rev. A (in press)]. These results show comparable intensities for J+=3/2 of the X 2Π3/2 ion and J+=1/2 of the X 2Π1/2 ion. Both transitions require an angular momentum change of ΔN=−1 upon photoionization. To provide further insight into the near‐threshold dynamics of this process, we also show rotationally resolved photoelectron angular distributions, alignment of the ion rotational levels, and rotational distributions for the parity components of the ion rotational levels. About 18% population is predicted to occur in the (+) parity component, which would arise from odd partial‐wave contributions to the photoelectron matrix element. This behavior is similar to that in (2+1) REMPI via the S(2) branch of the F 1Δ2 state of HBr and was shown to arise from significant l mixing in the electronic continuum due to the nonspherical molecular ion potential. Rotational ion distributions resulting from (2+1) REMPI via the S(10) branch of the F 1Δ2 state are also shown.
Show PACS
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.60.+q Photoelectron spectra
33.20.Sn Rotational analysis

Ru L‐edge x‐ray absorption studies of the formation of Ru–Cu bimetallic aggregates on Cu(100)

T. K. Sham, T. Ohta, T. Yokoyama, Y. Takata, Y. Kitajima, M. Funabashi, and H. Kuroda

J. Chem. Phys. 95, 8725 (1991); http://dx.doi.org/10.1063/1.461208 (7 pages) | Cited 1 time

Full Text: | Download PDF

Show Abstract
X‐ray absorption measurements at the Ru L3 edge have been used to study the adsorption of Ru3(CO)12 on Cu(100) surfaces at submonolayer and monolayer coverages and the subsequent formation of Ru–Cu bimetallic aggregates at these surfaces. The analysis of the Ru L3 edge x‐ray absorption near edge structure (XANES) reveals (a) the surface Ru–Cu bimetallic aggregates are three dimensional clusters of which the Ru atoms are in the ‘‘bulk’’ and the surface of the cluster is covered with Cu atoms, and (b) relative to pure Ru metal, Ru in the bimetallic aggregates gains d character. The chemical properties of these bimetallic surfaces and the effect of the cluster size on their electronic properties revealed by XANES as well as LEED and Auger are also reported. These results are compared with previous results of Ru3(CO)12/Cu(111). The implications of these observations are discussed.
Show PACS
68.55.-a Thin film structure and morphology
36.40.-c Atomic and molecular clusters
78.70.Dm X-ray absorption spectra
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Inertial axis reorientation in the S1←S0 electronic transition of 2‐pyridone. A rotational Duschinsky effect. Structural and dynamical consequences

A. Held, B. B. Champagne, and D. W. Pratt

J. Chem. Phys. 95, 8732 (1991); http://dx.doi.org/10.1063/1.461209 (12 pages) | Cited 68 times

Full Text: | Download PDF

Show Abstract
Rotationally resolved fluorescence excitation spectra of two vibronic bands in the S1←S0 electronic transition of 2‐hydroxypyridine (2HP), and of the corresponding bands in the hydroxy‐deuterated molecule, have been obtained. A comparison of the rotational constants of the two molecules shows that the two bands both originate in the zero‐point vibrational level of the planar keto tautomer of 2HP, 2‐pyridone (2PY), and terminate in different zero‐point levels of 2PY that have different out‐of‐plane equilibrium geometries at nitrogen. Additionally, all four bands exhibit ‘‘anomalous’’ rotational line intensities that are shown to result from an in‐plane inertial axis reorientation which occurs on absorption of the photon. Likely atomic displacements that are responsible for this ‘‘rotational’’ Duschinsky effect, which may have significant dynamical consequences in 2PY and other molecules, are discussed.
Show PACS
31.50.Df Potential energy surfaces for excited electronic states
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.50.Dq Fluorescence and phosphorescence spectra

Spectroscopy, dynamics, and chaos of the CS2 molecule: Fourier transform and phase‐space analysis

J. P. Pique, M. Joyeux, J. Manners, and G. Sitja

J. Chem. Phys. 95, 8744 (1991); http://dx.doi.org/10.1063/1.461210 (9 pages) | Cited 31 times

Full Text: | Download PDF

Show Abstract
In this paper we analyze the vibrational spectra of the Σ+g ground state of CS2, the experimental results of which have been described in a forth coming paper. We show that, up to 12 000 cm−1, CS2 can be described by a system of two degrees of freedom strongly coupled by a 1:2 type Fermi resonance. The corresponding vibrational spectra are refitted with the aid of only seven parameters. Analysis of the spectra by the statistical Fourier transform technique reveals stroboscopic effects between the symmetric stretching mode and the bending mode. The distinction between the ‘‘stroboscopic hole’’ due to these effects and the ‘‘correlation hole’’ due to nonintegrable terms in the Hamiltonian is discussed in detail. The study of the topology of the phase space of CS2 in the regular and chaotic cases is carried out in the basis described by a vibrational angular momentum which includes the Fermi resonance. We show the analogy between the localization of the wave packets of the eigenstates and the trajectories. We also show the destabilization of the trajectories due to a term in the Hamiltonian which couples neighboring polyads and which is a second Fermi resonance. We show that only two resonances are enough to induce a chaotic situation.
Show PACS
33.20.Tp Vibrational analysis
05.45.-a Nonlinear dynamics and chaos

Vibrationally resolved spectra of C2–C11 by anion photoelectron spectroscopy

D. W. Arnold, S. E. Bradforth, T. N. Kitsopoulos, and D. M. Neumark

J. Chem. Phys. 95, 8753 (1991); http://dx.doi.org/10.1063/1.461211 (12 pages) | Cited 169 times

Full Text: | Download PDF

Show Abstract
Anion photoelectron spectroscopy has been employed to obtain vibrationally resolved spectra of the carbon molecules C2–C11. The spectra of C−2–C−9 are dominated by linear anion to linear neutral photodetachment transitions. Linear to linear transitions contribute to the C−11 spectrum, as well. From these spectra, vibrational frequencies and electron affinities are determined for the linear isomers of C2–C9 and C11. The term value is also obtained for the first excited electronic state of linear C4. The spectra of C−10 and C−11 show evidence for transitions involving cyclic anions and/or neutrals. Similar types of transitions are identified in the spectra of other smaller molecules, specifically C−6, C−8, and to a lesser extent C−5.
Show PACS
33.60.+q Photoelectron spectra
33.20.Tp Vibrational analysis

Resonant two‐photon ionization spectroscopy of coinage metal trimers: Cu2Ag, Cu2Au, and CuAgAu

Gregory A. Bishea, Caleb A. Arrington, Jane M. Behm, and Michael D. Morse

J. Chem. Phys. 95, 8765 (1991); http://dx.doi.org/10.1063/1.461212 (14 pages) | Cited 15 times

Full Text: | Download PDF

Show Abstract
The jet‐cooled coinage metal triatomic molecules Cu2Ag, Cu2Au, and CuAgAu have been investigated using resonant two‐photon ionization spectroscopy. One band system, labeled as the math–math system, has been observed for each species, with origin bands at 13 188, 17 217, and 17 470 cm−1, respectively. Vibrational progressions have been assigned and vibrational constants have been extracted using a linear least‐squares fitting procedure. For Cu2Ag, 47 vibrational bands have been assigned within the math–math system. The upper states of these bands derive from combinations of two symmetric (a1) and one antisymmetric (b2) mode in the C2v point group. For the math–math system of Cu2Au, only seven vibrational bands have been observed, all occurring within a 500 cm−1 range. Lifetime measurements for the observed vibrational levels support the possibility that predissociation may be occurring in the math excited state of Cu2Au and this may be limiting the number of vibrational levels observed within this state. Finally, in the case of CuAgAu, 92 vibrational bands have been assigned, corresponding to excitations of three totally symmetric (a′) vibrational modes in the Cs point group. For this molecule, a complete set of vibrational frequencies (ωi) and anharmonicities (xij) have been obtained for the excited math state. In addition, the observation of weak hot bands in the spectrum permits the three vibrational modes of the math ground state to be characterized by ν1=222.83±0.29, ν2=153.27±0.22, and ν3=103.90±0.28 cm−1 for 63Cu107Ag197Au (1σ error limits).
Show PACS
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants

Resonant two‐photon ionization spectroscopy of jet‐cooled Au3

Gregory A. Bishea and Michael D. Morse

J. Chem. Phys. 95, 8779 (1991); http://dx.doi.org/10.1063/1.461213 (14 pages) | Cited 28 times

Full Text: | Download PDF

Show Abstract
A band system of jet‐cooled Au3 has been located in the near infrared region of the spectrum using resonant two‐photon ionization spectroscopy. The origin band is located at 13 354.15 cm−1 and the system extends more than 700 cm−1 further to the blue. The excited state displays a radiative lifetime of approximately 28 μs, corresponding to an absorption oscillator strength of f≊0.0003. Accordingly, it is thought that the transition corresponds to a spin‐forbidden doublet (S=1/2) to quartet (S=3/2) transition, which is made allowed by spin–orbit contamination, presumably in the upper state. A progression in a totally symmetric stretching vibration (ω=179.7 cm−1 ) is obvious in the spectrum, along with a much weaker progression in another mode, which displays an interesting pattern of splittings. Although no assignment is absolutely unambiguous, various candidates are presented. The most likely of these assigns the system as an math 4E′←math 2E′ transition in the D3h point group, with both the ground math 2E′ and excited math 4E′ states undergoing Jahn–Teller distortion. The vibronic levels of the math 4E′ state have been fitted assuming a linear Jahn–Teller effect in a system with both spin–orbit splitting and a significant anharmonicity in the Jahn–Teller active e′ vibrational mode. The combined effects of anharmonicity in the Jahn–Teller active mode and spin–orbit coupling appear not to have been previously investigated; they are therefore examined in some detail.
Show PACS
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.20.Ea Infrared spectra
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
36.40.-c Atomic and molecular clusters

A force field analysis of the methyl radical math 2A″2 state stretching potential using the local mode—coupled Morse oscillator model

S. G. Westre, X. Liu, J. D. Getty, and P. B. Kelly

J. Chem. Phys. 95, 8793 (1991); http://dx.doi.org/10.1063/1.461812 (10 pages) | Cited 10 times

Full Text: | Download PDF

Show Abstract
The local mode‐coupled Morse oscillator model was utilized to determine the quadratic, cubic, and quartic force constants for the vibrational stretching potential energy functions of the CH3, CD3, CH2D, and CHD2 using stretching fundamentals and overtones derived from resonance Raman studies. The Morse harmonic frequency and anharmonic constant of the methyl radical indicate that bonding in the methyl radical and a variety of ethylenic molecules is primarily a function of the sp2 hybridization of the central atom and that the bonding is not extensively influenced by the methyl radical’s unpaired electron or the π bonding in the ethylenic molecules. The vibrational states of the methyl radical are best described by wave functions containing significant amounts of normal mode character. The stretching frequencies for the tritiated methyl radical isotopomers are calculated.
Show PACS
34.20.Cf Interatomic potentials and forces
33.20.Tp Vibrational analysis

The Li2 C 1Πu state studied by a single‐frequency ultraviolet laser

Kiyoshi Ishikawa, Shunji Kubo, and Hajime Katô

J. Chem. Phys. 95, 8803 (1991); http://dx.doi.org/10.1063/1.461214 (6 pages) | Cited 11 times

Full Text: | Download PDF

Show Abstract
A newly constructed single‐frequency, autoscan laser spectrometer operating in the ultraviolet in combination with a collimated molecular beam has been used to obtain a high resolution fluorescence excitation spectrum in the region 30 850–31 400 cm−1. Eight hundred and seventy five rotational lines of the 7Li2 C 1Πu(v′=2–8)–X 1Σ+g and 6Li7Li C 1Π(v′=2–4)–X 1Σ+ transitions are assigned. The molecular constants of the C 1Πu state are determined and the potential curve is constructed using the Rydberg–Klein–Rees (RKR) method. By comparing the calculated Franck–Condon factors with the line intensities of the dispersed fluorescence spectrum, we determine the dependence of the electric dipole transition moment on the internuclear distance.
Show PACS
33.50.Dq Fluorescence and phosphorescence spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Sn Rotational analysis
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Observation of the visible absorption spectrum of H2O+

Biman Das and John W. Farley

J. Chem. Phys. 95, 8809 (1991); http://dx.doi.org/10.1063/1.461215 (7 pages) | Cited 11 times

Full Text: | Download PDF

Show Abstract
The math 2math1–math 2math1 system of H2O+ has been observed, using laser absorption spectroscopy in a velocity‐modulated discharge. A total of 78 transitions between 14 794 and 15 475 cm−1 have been observed with an uncertainty (1 SD) of 0.02 cm−1, including 76 transitions in the (0,7,0)–(0,0,0) band and 2 in the (0,8,0)–(0,0,0) band. This species is important for cometary astronomy, and intriguing for molecular physics because of its prominent Renner–Teller interaction. Careful measurements were made of the relative intensities of the absorption lines, which were measured to an accuracy of 13% (1 SD). This is the first observation of the math–math transition in absorption; all previous data were obtained in emission with conventional grating spectroscopy. The transition frequencies of our new data are in good agreement with previous work, and have improved accuracy. The new data have definite rejection of the interfering lines from excited neutral H2 that plagued previous work. Compared with previous work, the new data have the first quantitative measurement of intensities. The ratio of the Franck–Condon factors I8/I7=0.99±0.43 has been measured for the first time, where Iv=FCF[(0,v′,0)–(0,0,0)].
Show PACS
33.20.Kf Visible spectra
33.70.Fd Absolute and relative line and band intensities

Persistent infrared spectral hole burning of NO−2 ions in potassium halide crystals. I. Principle and satellite hole generation

W. P. Ambrose, J. P. Sethna, and A. J. Sievers

J. Chem. Phys. 95, 8816 (1991); http://dx.doi.org/10.1063/1.461216 (27 pages) | Cited 4 times

Full Text: | Download PDF

Show Abstract
New features are resolved within the internal vibrational mode spectra of NO−2 defects in KCl, KBr, and KI crystals at low temperatures using high‐resolution Fourier transform spectroscopy and persistent infrared spectral hole (PIRSH) burning separately and together. With interferometry it has been discovered that the vibrational linewidths of the different modes range over a factor of 300—from 0.01 cm−1 to ∼3 cm−1 and, with PIRSH burning, it has been demonstrated that the narrowest lines are inhomogeneously broadened while the broadest ones are homogeneously broadened. PIRSH’s have been found in some internal modes and combination bands of the NO−2 molecule when pumped with low‐intensity single‐mode lead salt diode lasers; however, detectable persistent holes are not produced in all of the modes because of a competition between hole production and relaxation by tunneling at low temperatures. This competition results in a hole burning intensity, below which hole relaxation overwhelms hole production and only small holes may be produced.
The most unusually shaped absorption features are the V‐shaped notches in the reorientational tunneling fine structure at the NO−2 bending mode frequency in KCl and KBr. Of all the internal modes that do show pronounced PIRSH burning, these V‐notched absorption bands exhibit the most striking behavior. Multiple satellite PIRSH’s are detected at frequencies away from the single‐mode laser burn frequency with a broadband probe beam produced by a high‐resolution Fourier transform interferometer. An explanation for these satellite holes is derived from temperature, plastic deformation, and uniaxial stress dependence measurements on the KCl@B:NO−2 absorption spectrum. We find that the inhomogeneous broadening of the KCl@B:NO−2 ν2 reorientational tunneling fine structure is dominated by degenerate rotor level splitting produced by random crystal strains. Degenerate perturbation theory of the rotor level splitting in the strain field is found to match very closely the V‐shaped inhomogeneous distribution of levels associated with the KCl@B:NO−2 reorientational tunneling fine structure. The general conclusion is that whenever strain splitting of a doubly degenerate level dominates the inhomogeneous broadening, then the absorption spectrum displays zero strength in the distribution at zero splitting and a linear increase in absorption coefficient away from this frequency generating the observed V‐shaped notch in the absorption profile.
Show PACS
78.20.-e Optical properties of bulk materials and thin films
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
63.20.Pw Localized modes

The effect of temperature on the luminescence from electron‐irradiated H2O ice

T. I. Quickenden, A. J. Matich, M. G. Bakker, C. G. Freeman, and D. F. Sangster

J. Chem. Phys. 95, 8843 (1991); http://dx.doi.org/10.1063/1.461217 (10 pages) | Cited 8 times

Full Text: | Download PDF

Show Abstract
The effect of temperature on the 385 nm luminescence band emitted by electron‐irradiated H2O ice has been determined between 79 and 117 K. From 79 to 101 K, the luminescence intensity did not change greatly with increasing temperature, but fell steeply between 101 and 117 K, paralleling the behavior of trapped OH. Kinetic analysis of the luminescence decay was possible in the 79–103 K region and revealed a long‐lived pseudo‐first‐order decay and a superimposed short‐lived decay with respective activation energies of 0.036±0.005 and 0.021±0.005 eV. The long‐lived emission is attributed to the migration of H+ to OH− formed from trapped OH, subsequent reaction producing H2O(C 1B1) which emits excimer luminescence when it falls to the dissociative A 1B1 state. This mechanism was tested by using it to derive a kinetic expression which relates the observed temperature dependencies of both the luminescence intensity and the decay rate. This mechanism suggests that the radiolytic yield of OH− in ice is in the vicinity of G(OH−)=0.2/100 eV.
Show PACS
82.50.Kx Processes caused by X-rays or γ-rays
61.80.Fe Electron and positron radiation effects

Rydberg states of NO in a magnetic field: Multichannel quantum defect approach of the linear Zeeman effect

Maurice Raoult, Stéphane Guizard, and Dolores Gauyacq

J. Chem. Phys. 95, 8853 (1991); http://dx.doi.org/10.1063/1.461218 (13 pages) | Cited 11 times

Full Text: | Download PDF

Show Abstract
The linear Zeeman effect for the nf and np Rydberg states of NO has been analyzed in the intermediate energy region (n=7 and n=15). This analysis is based on a multichannel quantum defect treatment (MQDT), including the magnetic interaction, as proposed by Monteiro and Taylor [T. S. Monteiro and K. T. Taylor, J. Phys. B: At. Mol. Phys. 22, L191 (1989)]. The nonpenetrating nf states exhibit almost no channel mixing, but they are significantly perturbed by the Zeeman interaction within each rotational channel in a moderate field of 1 T. An excellent agreement has been found between the experimental results obtained in a 1 T magnetic field and the calculations, showing in particular the first manifestation of the Paschen–Back effect in a molecule. The penetrating np states of NO exhibit channel interaction, but, on the other hand, they are less perturbed by a 1 T magnetic field than the nf states are. Theoretical predictions have been made for a larger field strength of 5 T in the case of the 7p and 15p states.
Show PACS
33.57.+c Magneto-optical and electro-optical spectra and effects
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Experimental study of the reactions of N2(A 3Σ+u) with H atoms and OH radicals

Grace H. Ho and Michael F. Golde

J. Chem. Phys. 95, 8866 (1991); http://dx.doi.org/10.1063/1.461219 (5 pages) | Cited 4 times

Full Text: | Download PDF

Show Abstract
The reactions of N2(A 3Σ+u) with H atoms and OH radicals have been studied by the discharge‐flow technique. The concentrations of the radicals were measured by resonance fluorescence and N2(A) was monitored by (A−X) emission. The rate constant of the N2(A)+H reaction was measured as (2.1±0.3)×10−10 cm3 s−1. Chemical reaction to NH+N was shown to be unimportant. The total rate constant for quenching of N2(A) by OH was measured as (1.1±0.4)×10−10 cm3 s−1. The channel leading to OH(2Σ+) has a rate constant of (1.0±0.3)×10−10 cm3 s−1. Approximately 16% of the OH(A) is formed in v′=1. The mechanisms of these two very rapid reactions are discussed.
Show PACS
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Theoretical study of the quenching of N2(A 3Σ+u) by hydrogen atoms

Robert F. Sperlein and Michael F. Golde

J. Chem. Phys. 95, 8871 (1991); http://dx.doi.org/10.1063/1.461220 (4 pages) | Cited 1 time

Full Text: | Download PDF

Show Abstract
Ab initio calculations on the interactions of N2(A 3Σ+u) and N2(X 1Σ+g) with H(1 2S) atoms in a T‐shape (C2v) geometry have been performed. The 2B2 state, resulting from the interaction of N2(A) with H, is strongly attractive, in contrast to the repulsive interaction of N2(X) with H in this geometry. When the C2v symmetry is relaxed, coupling of these two states in the vicinity of the ‘‘crossing region’’ is observed. The efficient quenching of N2(A) in collisions with H atoms is discussed in terms of the calculated properties of N2H.
Show PACS
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
31.70.Hq Time-dependent phenomena: excitation and relaxation processes, and reaction rates

Interpolated variational transition‐state theory: Practical methods for estimating variational transition‐state properties and tunneling contributions to chemical reaction rates from electronic structure calculations

Angels Gonzalez‐Lafont, Thanh N. Truong, and Donald G. Truhlar

J. Chem. Phys. 95, 8875 (1991); http://dx.doi.org/10.1063/1.461221 (20 pages) | Cited 86 times

Full Text: | Download PDF

Show Abstract
In many cases, variational transition states for a chemical reaction are significantly displaced from a saddle point because of zero‐point and entropic effects that depend on the reaction coordinate. Such displacements are often controlled by the competition between the potential energy along the minimum‐energy reaction path and the energy requirements of one or more vibrational modes whose frequencies show a large variation along the reaction path. In calculating reaction rates from potential‐energy functions we need to take account of these factors and—especially at lower temperatures—to include tunneling contributions, which also depend on the variation of vibrational frequencies along a reaction path. To include these effects requires more information about the activated complex region of the potential‐energy surface than is required for conventional transition‐state theory. In the present article we show how the vibrational and entropic effects of variational transition‐state theory and the effective potentials and effective masses needed to calculate tunneling probabilities can be estimated with a minimum of electronic structure information, thereby allowing their computation at a higher level of theory than would otherwise be possible. As examples, we consider the reactions OH+H2, CH3+H2, and Cl+CH4 and some of their isotopic analogs. We find for Cl+CH4→HCl+CH3 that the reaction rate is greatly enhanced by tunneling under conditions of interest for atmospheric chemistry.
Show PACS
82.20.Db Transition state theory and statistical theories of rate constants
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Energetics and dynamics in the dissociative photoionization of PF3 at 21.2 eV

David J. Reynolds, Eddy H. van Kleef, and Ivan Powis

J. Chem. Phys. 95, 8895 (1991); http://dx.doi.org/10.1063/1.461222 (6 pages) | Cited 9 times

Full Text: | Download PDF

Show Abstract
The first five electronically excited states of PF+3 generated by He i photoionization are found to dissociate exclusively to PF+2 with dynamically distinct mechanisms. A pronounced correlation is observed between the direction of ejection of the photoelectron and the photofragment ion which issue from individual photoionization events, from which it is inferred that both the photoelectron emission and the subsequent unimolecular ion dissociation are highly anisotropic processes. Measurement of the kinetic energy which accompanies PF+2 formation at its experimental onset is used to identify the preferred thermochemical threshold value for this ion.
Show PACS
33.80.Eh Autoionization, photoionization, and photodetachment
82.20.Hf Product distribution

Theoretical studies of the reaction dynamics of the matrix‐isolated F2+cis‐d2 ‐ethylene system

Lionel M. Raff

J. Chem. Phys. 95, 8901 (1991); http://dx.doi.org/10.1063/1.461223 (18 pages) | Cited 32 times

Full Text: | Download PDF

Show Abstract
The molecular dynamics of the F2+cis‐d2 ‐ethylene addition reaction and the subsequent decomposition dynamics of the vibrationally excited 1,2‐difluoroethane‐d2 product isolated in Ar or Xe matrices at 12 K are investigated using trajectory methods that incorporate nonstatistical sampling to enhance the reaction probabilities. The matrix is represented by a face‐centered‐cubic crystal containing 125 unit cells with 666 lattice atoms in a cubic (5×5×5) arrangement. Both interstitial and substitutional sites for the F2/cis‐d2 ‐ethylene pair are examined. Transport effects of the bulk are simulated using the velocity reset method introduced by Riley, Coltrin, and Diestler [J. Chem. Phys. 88, 5934 (1988)]. The potential‐energy hypersurface for the system is written as the separable sum of a lattice potential, a lattice–substrate interaction, and a gas‐phase potential for 1,2‐difluoroethane‐d2. The first two of these have pairwise form, while the 1,2‐difluoroethane‐d2 potential is identical to that employed previously to study the unimolecular reaction dynamics of matrix‐isolated 1,2‐difluoroethane‐d4 [J. Chem. Phys. 93, 3160 (1990)].
The major F2+cis‐d2 ‐ethylene reaction mechanism involves a four‐center, concerted αβ addition across the C=C double bond. A small contribution from an atomic addition mechanism that initially forms fluoroethyl and fluorine radicals is observed in a xenon matrix, but not in argon. Subsequent to the formation of 1,2‐difluoroethane‐d2, the observed dynamic processes are vibrational relaxation to the lattice phonon modes, orientational exchange, and HF or DF elimination reactions. Vibrational relaxation is found to be very similar to that observed previously for 1,2‐difluoroethane‐d4. The process is well described by a first‐order rate law with rate coefficients in the range 0.046–0.069 ps−1. The distribution of rate coefficients, as well as the averages, are nearly identical for Ar and Xe lattices. Very little difference is found between the relaxation rates for 1,2‐difluoroethane‐d2 and those for the HF(DF)+fluoroethylene products. The propensity for 1,2‐difluoroethane‐d2 to undergo orientational exchange increases as the available free space in the lattice decreases.
Thus, it is a more important process in Ar than in Xe matrices. For the same reason, it occurs with greater frequency when the reactants are in an interstitial site than when they are substitutionally held. The probability of HF or DF elimination increases as the available free space in the matrix cage decreases. The relaxation rates show that this effect is not the result of different energy transfer rates. At least five distinct mechanisms play a role in HF and DF elimination reactions in the face‐centered‐cubic lattice. These are, in order of importance (a) αβ addition followed by syn elimination; (b) hydrogen‐ or deuterium‐atom transfer to fluorine on the adjacent carbon followed by a protracted delay prior to C–F bond rupture; (c) rotation about the C=C double bond in the fluoroethylene product; (d) reversible hydrogen‐ or deuterium‐atom transfer; and (e) atom addition with intervening delay. The computed elimination yield ratios between matrices are in good agreement with the experimental values. The calculated cis/trans ratio of fluoroethylenes formed subsequent to HF elimination in Ar are a factor of 2.7 lower than those observed in the experiments. The stabilization ratios are much larger than the experimental values. These results are interpreted to mean that the experimental matrix environment is more open and spacious than that for the crystal structure used in the calculations.
Show PACS
82.30.Nr Association, addition, insertion, cluster formation
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Fd Collision theories; trajectory models
82.20.Tr Kinetic isotope effects including muonium

Icosahedral structure in hydrogenated cobalt and nickel clusters

T. D. Klots, B. J. Winter, E. K. Parks, and S. J. Riley

J. Chem. Phys. 95, 8919 (1991); http://dx.doi.org/10.1063/1.461224 (12 pages) | Cited 46 times

Full Text: | Download PDF

Show Abstract
Reactions with ammonia and with water are used to probe the geometrical structures of cobalt and nickel clusters that are saturated with hydrogen. Ammonia saturation experiments allow the determination of the number of primary NH3 binding sites on cluster surfaces, and this number shows a repeated minimization to values of 12 for many cluster sizes in the 50‐ to 200‐atom size region. These sizes correspond to closed shells and subshells of icosahedra, suggesting that the ammoniated clusters have metal frameworks with icosahedral structure. The equilibrium reaction of the hydrogenated clusters with a single water molecule shows a pattern of local maxima in the cluster–water binding energy, with the maxima in most cases coming at clusters having one metal atom more than those showing minima in ammonia binding. This correlation suggests that nonammoniated clusters likewise have icosahedral structure, and is consistent with the nature of the metal–water interaction. Some of the larger clusters do not show clear evidence for icosahedral structure at room temperature, although they begin to do so at elevated temperature. Annealing experiments suggest that many of these clusters are icosahedral in their most stable configuration at room temperature, although the 147‐atom nickel cluster is not. In general, hydrogenation enhances the icosahedral features in the ammonia and water binding patterns compared to those seen for bare clusters, and extends the cluster size region over which icosahedral structure is evident.
Show PACS
36.40.-c Atomic and molecular clusters
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.90.+j Other topics in physical chemistry and chemical physics (restricted to new topics in section 82)

Quantum study of the redistribution of flux during inelastic collisions

Millard H. Alexander

J. Chem. Phys. 95, 8931 (1991); http://dx.doi.org/10.1063/1.461225 (10 pages) | Cited 25 times

Full Text: | Download PDF

Show Abstract
A new method is presented for the study of the mechanism of inelastic atomic and molecular collisions. This involves the determination of the current density associated with, separately, the incoming and outgoing scattering wave functions in either an asymptotic (diabatic) or locally adiabatic basis. This yields a picture of how the incoming flux, initially associated with a given internal state, redistributes itself as a function of the interparticle separation both as the particles approach, and, subsequently, as the particles recede. It is shown that the separation into incoming and outgoing flux, which is valid asymptotically, continues to be valid as the collision partners approach, without mixing of the contributions from the incoming and outgoing waves. A simple extension of our linear‐reference‐potential, log‐derivative propagation technique can be used to compute the redistribution of the initial flux. It is argued that analysis in a fully adiabatic basis, which corresponds to the local eigenvectors of the collision system, provides the most meaningful physical insight. A simple stabilization correction can be introduced, which prevents adiabatically closed channels from numerically contaminating the determination of flux redistribution among the locally open channels. Application is made to a pedagogical two‐state problem, to a multistate collision system involving four different electronic potential curves, and to a second multistate collision system involving a closed‐channel resonance.
Show PACS
34.50.-s Scattering of atoms and molecules
03.65.-w Quantum mechanics

Fine‐structure selective collisional energy transfer in spherical top molecules: Evidence for a symmetry‐based mechanism from rovibrational eigenfunctions

Robert Parson

J. Chem. Phys. 95, 8941 (1991); http://dx.doi.org/10.1063/1.461226 (21 pages) | Cited 16 times

Full Text: | Download PDF

Show Abstract
Recent state‐resolved experiments have shown that rotational energy transfer in collisions of vibrationally excited spherical top molecules is remarkably selective with respect to the fine structure components of the rovibrational states. In a recent paper [J. Chem. Phys. 93, 8731 (1990)], these results were rationalized on the basis of symmetry arguments and the Harter–Patterson theory of spectral clustering. The present paper provides numerical evidence for those assertions. Matrix elements of an atom–spherical top interaction potential are calculated using numerically accurate wave functions from spectroscopic Hamiltonians and using the approximate wave functions given by the Harter–Patterson theory. Agreement between the two calculations is satisfactory and both confirm the propensity rules derived previously, suggesting that the proposed mechanism does in fact operate in these systems.
Show PACS
34.50.Ez Rotational and vibrational energy transfer
34.50.-s Scattering of atoms and molecules

Vibrational‐state selective cross sections for the charge transfer H++HCl(X 1∑+)→H(2Sg)+HCl+(A 2∑+,v′)

Th. Glenewinkel‐Meyer and Ch. Ottinger

J. Chem. Phys. 95, 8962 (1991); http://dx.doi.org/10.1063/1.461227 (8 pages) | Cited 7 times

Full Text: | Download PDF

Show Abstract
Vibrational‐state selective cross sections have been measured for the endothermic charge‐transfer reactions H+,D++HCl(X 1∑+)→H,D(2Sg)+HCl +(A 2∑+,v′)−2.67 eV, for collision energies up to 1 keV by means of detecting the spontaneous optical emission of the HCl+(A 2∑+,v′→X 2Πi, v″) band system. Absolute values between 0.25 and 1 Å2 were obtained by calibration against the known cross section for electron‐impact ionization of N2 with subsequent emission of the N+2(B,v′→X,v″) transition. The charge‐transfer cross sections were also calculated using the Landau–Zener theory. The required model parameters were derived from recent ab initio calculations. The energy dependence and the relative magnitude of the cross sections for the product vibrational levels v′=0–5 were closely rendered by the theoretical curves in the velocity range where the Landau–Zener approach applies, i.e., below 200 km/s (≡200 eV for protons). The absolute magnitude of the calculated cross sections also agrees with the measurements within the experimental error limits.
Show PACS
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
Page 1 of 4 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close