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

You Tube Flickr Twitter UniPHY Group iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue

15 Dec 1983

Volume 79, Issue 12, pp. 5735-6430

Page 1 of 4 Pages Next Page | Jump to Page

Electric dipole intensity parameters for lanthanide 4f → 4f transitions

Michael F. Reid and F. S. Richardson

J. Chem. Phys. 79, 5735 (1983); http://dx.doi.org/10.1063/1.445760 (8 pages) | Cited 71 times

Full Text: | Download PDF

Show Abstract
A general parametrization scheme for the electric dipole intensities of lanthanide 4f → 4f crystal‐field transitions is proposed. This parametrization is sufficiently general to accommodate any 4f → 4f intensity mechanism based on the ‘‘one‐electron’’ and ‘‘one‐photon’’ approximations for lanthanide‐ligand‐radiation field interactions. It includes as a subset, the familiar Judd–Ofelt–Axe intensity parameters, AtpΞ(t, λ), but introduces additional parameters which are shown to be essential in cases where the lanthanide‐ligand pairwise interactions cannot be assumed to be cylindrically symmetric. Expressions are given for calculating the general intensity parameters in terms of two specific intensity mechanisms. Special consideration is given to the effects of ligand polarizability anisotropy on the intensity parameters. A set of ‘‘intrinsic’’ intensity parameters are also introduced. These parameters are defined within the context of the ‘‘superposition’’ model for lanthanide‐ligand interactions, and are independent of coordination geometry and lanthanide site symmetry.
Show PACS
71.70.Ch Crystal and ligand fields
78.40.Ha Other nonmetallic inorganics

Comparison of calculated and experimental 4f → 4f intensity parameters for lanthanide complexes with isotropic ligands

Michael F. Reid, John J. Dallara, and F. S. Richardson

J. Chem. Phys. 79, 5743 (1983); http://dx.doi.org/10.1063/1.445761 (9 pages) | Cited 43 times

Full Text: | Download PDF

Show Abstract
Calculations of 4f → 4f electric dipole intensity parameters are reported for six different lanthanide (III) systems whose solid‐state structures and optical spectra have been well characterized. In each case, the ligands are considered to have isotropic electronic charge distributions, and the 4f → 4f intensity parametrization is expressed in terms of the parameters Aλλ±1,p(λ=2, 4, and 6), which have been defined in a previous paper (see paper I). The calculations include contributions to these parameters from both the static‐coupling and dynamic‐coupling intensity mechanisms. Comparisons between the calculated and empirically determined signs of the Aλλ±1,p parameters suggest that, in most cases, the dynamic‐coupling mechanism makes the dominant contributions to the Aλλ+1,p parameters. The empirically determined signs of the Aλλ−1,p parameters correlate with those calculated on the basis of the static‐coupling mechanism. For isotropic ligands, the dynamic‐coupling mechanism cannot contribute to the Aλλ−1,p parameters. Intrinsic intensity parameters, defined within the context of the mechanism‐independent superposition model for lanthanide‐ligand interactions, are also derived for each of the six systems examined here. These parameters, denoted herein as mathλλ±1, are defined to be independent of coordination number, coordination geometry, and lanthanide site symmetry.
Show PACS
71.70.Ch Crystal and ligand fields
78.40.Ha Other nonmetallic inorganics

Spin density distributions and g values in semiquinones

B. S. Prabhananda

J. Chem. Phys. 79, 5752 (1983); http://dx.doi.org/10.1063/1.445762 (6 pages) | Cited 10 times

Full Text: | Download PDF

Show Abstract
From a study of several semiquinone systems, we have shown that their g values can be expressed in terms of the π‐electron spin densities on the oxygens by a linear equation. This suggests the possibility of estimating the spin densities on the oxygens directly from the g values in similar systems. The spin density distribution used in establishing such a relation had been determined with the help of a new set of Q parameters for the 13C and 17O hyperfine splittings associated with the C′2CO fragment. Recognition of the existence of hydrogen bonds in solvents such as water or ethanol, by introducing an additional parameter QOOH is a new feature of this work. Q0OH=6.0 G in water or ethanol. QOOH=0 in aprotic solvents. Reliability of our Q parameters and the spin density distributions determined with their help, has been demonstrated by comparing the predicted and the observed hyperfine splittings/spin densities, not only in semiquinones, but also in 2,4,6 tri‐t‐butyl phenoxy radical and in benzophenone potassium ketyl. (Other authors have recommended substantially different sets of Q parameters.) It has been possible to estimate QCCC′=22.2 G, for sp3 hybridized C″ as in −C″H3, using the spin density distribution in durosemiquinone (DSQ−). Spin densities in DSQ− in ethanol were obtained with the help of our g values. Our value of QCCC″ is considerably less than the theoretical estimate of Strauss and Fraenkel, but is consistent with the predictions of Fessenden.
Show PACS
76.30.Rn Free radicals

Numerical simulation of the coherent anti‐Stokes Raman scattering spectrum of CO2

N. Papineau and M. Péalat

J. Chem. Phys. 79, 5758 (1983); http://dx.doi.org/10.1063/1.445763 (11 pages) | Cited 14 times

Full Text: | Download PDF

Show Abstract
A CARS spectrum of natural CO2 under normal conditions of temperature and pressure has been recorded in the 1210–1480 cm−1 range with a resolution of 0.07 cm−1. We have observed the Q branches of the fundamental bands ν1 and 2ν2 of the different species of natural CO2 and several hot bands of the isotopic species 12C 16O2. We have also assigned the O and S lines, for all these bands, and some of the weak P and R lines of the first hot bands. A theoretical calculation of line positions and intensities has been performed taking into account Fermi resonance as well as l‐type doubling and Coriolis interaction. For the Q branches we have made a calculation with due account for motional narrowing. The entire spectrum has thus been simulated and the agreement with the experimental spectrum is excellent.
Show PACS
33.20.Fb Raman and Rayleigh spectra (including optical scattering)

Resonant two‐photon ionization of fluorene rare‐gas van der Waals complexes

Samuel Leutwyler@f@f, Uzi Even, and Joshua Jortner

J. Chem. Phys. 79, 5769 (1983); http://dx.doi.org/10.1063/1.445764 (11 pages) | Cited 49 times

Full Text: | Download PDF

Show Abstract
Resonant two‐photon ionization combined with time‐of‐flight mass spectrometry was applied for the interrogation of the S0 → S1 electronic‐vibrational excitations of van der Waals complexes of fluorene (FL) with rare‐gas atoms and N2 in supersonic jets. Energy‐resolved and mass‐resolved spectra of FL ⋅ Ne, FL ⋅ Arn (n=1–3), FL ⋅ Kr, FL ⋅ Xe, and FL ⋅ N2 were recorded over the energy range 0–800 cm−1 above the electronic origin of S1. The red microscopic spectral shifts of the electronic origins of FL ⋅ R (R=Ar, Kr, and Xe) complexes are dominated by dispersive interactions, being proportional to the polarizability of R. The vibrational level structure of FL ⋅ Rn (R=Ar, Kr, and Xe) complexes exhibits intramolecular vibrational excitations of FL, as well as intermolecular vibrations, which involve the relative motion of FL and R in the complex. The spectra of FL ⋅ Ne and FL ⋅ N2 reveal a rich vibrational structure in the vicinity of the electronic origin, indicating a substantial change of the nuclear configuration upon electronic excitation. Upper and lower bounds on the dissociation energies of FL ⋅ R (R=Ne, Kr, and Xe) and FL ⋅ Ar2 were inferred from the vibrational level structure in the mass‐resolved spectra, where the disappearance of the signal of the parent van der Waals ion and the appearance of the ion signal of the fragments mark the onset of the vibrational predissociation process.
Show PACS
33.20.Kf Visible spectra
33.80.Gj Diffuse spectra; predissociation, photodissociation

Spectral moments of vibrationally excited components of continuous vibronic spectra

Jeffrey A. Joens and Edward J. Bair

J. Chem. Phys. 79, 5780 (1983); http://dx.doi.org/10.1063/1.445765 (5 pages) | Cited 6 times

Full Text: | Download PDF

Show Abstract
The spectral absorption coefficient of a continuous vibronic system is a composite of contributions which change according to the population of the vibrational levels of the lower electronic state. These components have distinctive shapes related to the shape of the vibrational wave function for a particular mode of the lower state. In addition, the component from each level of the lower electronic state is characterized by an average spectral frequency, or first spectral moment, observed as a shift from the position of the spectrum of molecules which are not vibrationally excited. The spectral moments can be calculated from sum rules. The present paper compares the spectral shifts observed in thermally excited spectra of Cl2, OCS, and O3 with those calculated using different approximations to the sum rules to examine the relative importance of: (a) the relative frequencies of the upper and lower states; (b) changes in the electronic transition moment with vibrational excitation; (c) anharmonicity; or (d) anharmonic mode coupling. It is found that each of these effects can be important, or even dominant, in individual cases.
Show PACS
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.20.Lg Ultraviolet spectra
33.20.Kf Visible spectra

Electron spin‐echo modulation effects in disordered systems: Structure of traps for H and D atoms in frozen water solutions based on 1H and 2D nuclear modulation data

S. A. Dikanov, Yu. D. Tsvetkov, A. V. Astashkin, and A. A. Shubin

J. Chem. Phys. 79, 5785 (1983); http://dx.doi.org/10.1063/1.445766 (11 pages) | Cited 7 times

Full Text: | Download PDF

Show Abstract
Modulation effects induced by matrix protons and deuterons in the primary ESE from H and D atoms trapped in frozen water solutions of sulfuric acid have been analyzed. It has been shown that the nuclear quadrupole interaction in a deuterated sample additionally damps the modulation.
Show PACS
76.30.Mi Color centers and other defects
76.60.Lz Spin echoes

Magnetic vibrational circular dichroism of methyl halides in solution

T. R. Devine and T. A. Keiderling

J. Chem. Phys. 79, 5796 (1983); http://dx.doi.org/10.1063/1.445767 (6 pages) | Cited 21 times

Full Text: | Download PDF

Show Abstract
The magnetic vibrational circular dichroism of four methyl halides in CCl4 solution has been measured. Contrary to expectations based on available theoretical models for MVCD, predominantly B‐term MVCD is found for both the A1 and E C–H stretching vibrations. MVCD of these two modes are opposite in sign for each of the CH3X species, and their relative intensity and ΔA/A values vary systematically with halogen mass. Similar results are found in the CH3 deformation region. MVCD of the N–H stretches in NH3 is also presented for sake of comparison.
Show PACS
33.20.Ea Infrared spectra
33.55.+b Optical activity and dichroism
33.57.+c Magneto-optical and electro-optical spectra and effects

Low temperature spectroscopy of internally hydrogen‐bonded 2‐(2′‐hydroxy‐5′‐methylphenyl)‐benzotriazole in a mixed crystal@fa@f)

David F. Bocian@f@f, Alan L. Huston@f@f, and Gary W. Scott@f@f

J. Chem. Phys. 79, 5802 (1983); http://dx.doi.org/10.1063/1.445768 (6 pages) | Cited 12 times

Full Text: | Download PDF

Show Abstract
Low temperature fluorescence and fluorescence excitation spectra of 2‐(2′‐hydroxy‐5′‐methylphenyl)‐benzotriazole (MeHPB) in a single crystal biphenyl host are reported which exhibit sharp vibrational structure. The spectra are analyzed in terms of seven vibrational modes including three phenyl modes, three normal modes involving N–N and C–N stretching and bending motion, and a low frequency torsional vibration about the central C–N bond. The fluorescence exhibits a normal Stokes shift indicating that excited‐state intramolecular proton transfer is precluded in this mixed crystal probably because the MeHPB molecule is held in a nonplanar conformation by molecular packing forces. A model of the MeHPB molecule based on semiempirical molecular orbital calculations is also presented which provides support for these conclusions.
Show PACS
78.55.Kz Solid organic materials
78.40.Ha Other nonmetallic inorganics

Raman studies in CuTCNQ: Resonance Raman spectral observations and calculations for TCNQ ion radicals

Efstratios I. Kamitsos and William M. Risen

J. Chem. Phys. 79, 5808 (1983); http://dx.doi.org/10.1063/1.445769 (12 pages) | Cited 31 times

Full Text: | Download PDF

Show Abstract
The Raman spectra of thin film, and powdered crystalline forms of CuTCNQ have been studied and analyzed in connection with their electronic spectra and vibrational normal coordinate analysis and molecular orbital results. Nonresonance and resonance Raman conditions have been obtained by using different sample forms and source wavelengths. Shifts of TCNQ− and TCNQ= vibrational frequencies from those of TCNQ0 due to changes in the charge on the TCNQ moiety have been calculated in terms of molecular orbital parameters and TCNQ0 vibrational frequencies. The resonance Raman enhancement of TCNQ− in the red band system is shown to be of Franck–Condon origin and its resonance Raman spectrum in this region is calculated. Transformation of CuTCNQ to TCNQ0 with different laser lines is explained on the basis of photoinduced electronic transitions.
Show PACS
75.20.Ck Nonmetals
78.30.Jw Organic compounds, polymers

Properties of Sc3, Y3, and Sc13 molecules at low temperatures, as determined by ESR

L. B. Knight, R. W. Woodward, R. J. Van Zee, and W. Weltner

J. Chem. Phys. 79, 5820 (1983); http://dx.doi.org/10.1063/1.445751 (8 pages) | Cited 52 times

Full Text: | Download PDF

Show Abstract
Sc3 and Y3 molecules have been isolated in rare gas matrices at temperatures near 4 K. ESR spectra establish that the structure of Sc3 is an equilateral triangle at 4–30 K with a 2A′1 ground state. The possibility remains that Sc3 is a fluxional bent molecule with a very low barrier to pseudorotation. The 45Sc hyperfine splitting indicates that the unpaired electron has little s character and is delocalized in 3d orbitals on the three equivalent atoms. Y3, however, is not equilateral and is most probably a bent molecule at these temperatures with the spin again distributed over the 3d atomic orbitals, but in a 2B2 ground state. La3 was not observed and is therefore judged to be a linear orbitally degenerate molecule. Under special conditions, a cluster of exceptional stability Scx, where x ≥ 9 is formed in neon matrices. From its uniqueness and from the hyperfine structure in its ESR spectrum, it is suggested that it may be Sc13 with an icosahedral structure. This places 12 equivalent atoms at the vertices and one at the center of the icosahedron and leads to a 2Ag ground state. However, Scx as observed at 4 K could also be a dynamic Jahn–Teller molecule with only a small barrier between its distorted conformations.
Show PACS
33.35.+r Electron resonance and relaxation
36.40.-c Atomic and molecular clusters

The microwave spectra of CH2DSH and CHD2SH@fa@f)

Chun Fu Su@f@f and C. Richard Quade

J. Chem. Phys. 79, 5828 (1983); http://dx.doi.org/10.1063/1.445752 (7 pages) | Cited 3 times

Full Text: | Download PDF

Show Abstract
The microwave torsional‐rotational spectra of CH2DSH and CHD2SH have been measured and analyzed over the frequency range 12.5–48.0 MHz. a‐, b‐, and c‐dipole transitions have been assigned for both species which makes it possible to determine the tunneling frequency between the two gauche torsional levels for both species. An internal rotation analysis gives the torsional potential energy coefficients V1=−3.40±0.10 cm−1, V3=456.3±0.5 cm−1 for CH2DSH and V1=4.45±0.10 cm−1, V3=424.5±0.5 cm−1 for CHD2SH with V2 constrained to zero.
Show PACS
33.20.Bx Radio-frequency and microwave spectra
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Vibrational dephasing in molecular mixed crystals: A picosecond time domain CARS study of pentacene in naphthalene and benzoic acid

Koos Duppen, D. P. Weitekamp, and Douwe A. Wiersma

J. Chem. Phys. 79, 5835 (1983); http://dx.doi.org/10.1063/1.445753 (10 pages) | Cited 20 times

Full Text: | Download PDF

Show Abstract
Multiresonant time‐domain coherent anti‐Stokes Raman scattering (CARS) experiments have been employed in a study of the decay of vibrational coherences of pentacene doped into naphthalene and benzoic acid. In all cases, the CARS decay is found to be exponential, which indicates that the electronic and vibronic inhomogeneities in this system are strongly correlated. The temperature dependence of vibrational dephasing shows no effect of coupling to the lowest‐frequency librational mode of pentacene that is known to dominate electronic dephasing. This surprising result can be understood on basis of a dephasing model where rapid coherence exchange exists between a cold vibrational transition and a corresponding near‐resonant librationally hot one. For the 767 cm−1 vibrational transition, oscillations of the CARS signal as a function of delay are shown to arise from interference at the detector with a nearby naphthalene host signal. An inconsistency with a previously reported spontaneous Raman study is resolved by showing that the signal observed there is actually site‐selected fluorescence.
Show PACS
78.30.Jw Organic compounds, polymers

Energy up‐conversion in LaF3:Nd3+

B. R. Reddy and P. Venkateswarlu

J. Chem. Phys. 79, 5845 (1983); http://dx.doi.org/10.1063/1.445754 (6 pages) | Cited 24 times

Full Text: | Download PDF

Show Abstract
On resonant excitation of the D levels of LaF3:Nd3+ with yellow laser line, ultraviolet fluorescence is detected from L levels. It is found that both sequential two photon excitation (STEP) process and energy transfer up‐conversion (ETU) process are responsible for the population drain mechanism from the lower D levels to the higher L levels. A rate equation model has been developed which also supported the ETU process.
Show PACS
78.55.Hx Other solid inorganic materials
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Singlet–triplet perturbations in the math 1A2 (v=0) state of thioformaldehyde

D. J. Clouthier, D. A. Ramsay, and F. W. Birss

J. Chem. Phys. 79, 5851 (1983); http://dx.doi.org/10.1063/1.445755 (12 pages) | Cited 18 times

Full Text: | Download PDF

Show Abstract
Extensive singlet–triplet perturbations have been observed in the 0–0 band of the math 1A2–math 1A1 system of H2CS with energy displacements up to about 0.4 cm−1. The singlet–triplet nature of the perturbation has been confirmed by high resolution magnetic rotation studies and by laser excitation studies in the presence of a magnetic field. The J and Ka dependence of the perturbation matrix elements has been shown to be consistent with a vibronic spin‐orbit mechanism. The coupling is predominantly to the F1 components of the 4361 level of the math 3A2 state.
Show PACS
33.80.Be Level crossing and optical pumping
33.20.Lg Ultraviolet spectra
33.55.+b Optical activity and dichroism
33.57.+c Magneto-optical and electro-optical spectra and effects

Low‐frequency Raman spectrum of supercooled water

S. Krishnamurthy, R. Bansil, and J. Wiafe‐Akenten

J. Chem. Phys. 79, 5863 (1983); http://dx.doi.org/10.1063/1.445756 (8 pages) | Cited 69 times

Full Text: | Download PDF

Show Abstract
We report measurements of the Raman spectrum of supercooled water in the hindered translational region (20–400 cm−1) down to a temperature of −20 °C. The spectra are analyzed after correcting for the effects of Boltzmann factor and harmonic oscillator coupling, i.e., in the reduced R(ν) representation of Shuker and Gammon. Spectral deconvolution shows that in addition to the previously observed 0‐0‐0 bending mode (≂60 cm−1) and the 0‐0 stretching mode (≂190 cm−1), there is a weak feature at 260 cm−1 whose intensity increases by almost an order of magnitude as temperature decreases from 40 to −20 °C. A plausible interpretation of the 260 cm−1 band is that it is analogous to the 310 cm−1 band seen in ice I and probably arises because of differing electrostatic interactions in different configurations of coupled H bonds of neighboring H2O molecules. The 0‐0 stretching band at 190 cm−1 changes in many respects as temperature decreases from 40 to −20 °C: (i) Its peak intensity increases almost four times; (ii) integrated intensity increases three times; (iii) bandwidth decreases about 30%; and (iv) peak maximum increases linearly from 176 cm−1 at 40 °C to 202 cm−1 at −20 °C. In contrast, the 0‐0‐0 bending at 60 cm−1 is quite insensitive to changes in temperature. The increase in the intensity of the 190 and 260 cm−1 bands is consistent with the idea that four‐coordinated H2O molecules contribute directly to these spectral features and the fraction of such molecules increases with decreasing temperature. This effect on intensity is further enhanced by the strong coupling of the motion of a few four‐coordinated water molecules, as seen in the small‐angle x‐ray scattering data of Bosio et al. We also observe a limiting value to the width of the 190 cm−1 band at temperatures below the melting point, suggesting that the local structure of supercooled water is approaching some limiting structure.
Show PACS
78.30.C- Liquids
33.20.Fb Raman and Rayleigh spectra (including optical scattering)

Emission, optical–optical double resonance, and excited state absorption spectroscopy of matrix isolated chromium and molybdenum atoms@fa@f)

M. J. Pellin, D. M. Gruen, T. Fisher@f@f, and T. Foosnaes@f@f

J. Chem. Phys. 79, 5871 (1983); http://dx.doi.org/10.1063/1.445757 (16 pages) | Cited 7 times

Full Text: | Download PDF

Show Abstract
Making use of a combination of time‐resolved emission, optical–optical double resonance, and excited state absorption spectroscopy, it has been possible to assign virtually all spectral features with energies below the z7P0 state of matrix isolated Cr atoms. The a5S state located at 7593 cm−1 in the free gaseous Cr atom has lifetimes of 6.32 and 5.1 s in Ar and Kr matrices, respectively. Matrix perturbations on Cr emission lines are small (<±100 cm−1). The dependence of nonradiative decay rates on the local density of states is elucidated. The magnitude of matrix shifts for a particular transition is correlated with the electronic configurations of ground and excited states and it is pointed out that states having only ‘‘s’’ electrons in addition to ‘‘d’’ electrons maintain their gas phase energy relationships in the matrix environment. Direct fluorescence is observed from the z7P0 level of Mo to the 7s ground state. The spin‐orbit splitting of the ‘‘relaxed’’ z7P0 state is 690 cm−1, slightly lower than the 707 cm−1 splitting of the free gaseous Mo atom.
Show PACS
32.50.+d Fluorescence, phosphorescence (including quenching)
32.30.Jc Visible and ultraviolet spectra

Emission, ground, and excited state absorption spectroscopy of Cr2 isolated in Ar and Kr matrices@fa@f)

M. J. Pellin and D. M. Gruen

J. Chem. Phys. 79, 5887 (1983); http://dx.doi.org/10.1063/1.445758 (7 pages) | Cited 12 times

Full Text: | Download PDF

Show Abstract
Irradiation into either of the two resonance transitions of Cr atoms in Kr matrices results in strong bleaching of the atomic absorptions and simultaneous growth of two Cr2 dimer bands. The lower energy band of Cr2 at ∼470 nm is the well‐known 1Σ+u → 1Σ+g transition. The higher energy band at ∼340 nm we assign to the 1Πu ← 1Σ+g transition which occurs at almost the same energy as, and is therefore obscured by, the y7P0 ← a7S transition of normally present Cr atoms in Kr (and Ar) matrices. Laser induced fluorescence from the ∼470 nm band gives a broad, featureless emission presumably because of extensive predissociation after cage relaxation of the excited 1Σ+u state. Emission after excitation of 1Πu ← 1Σ+g transition yields a four member progression with spacing of ∼240 cm−1. The spectrum is consistent with emission from a 3Σg ‘‘trap’’ level to a lower lying 3Σu state, ∼8000 cm−1 above ground. An energy level diagram of the Cr2 molecule is presented which incorporates all of the spectroscopic information available on the dimer.
Show PACS
33.50.Dq Fluorescence and phosphorescence spectra
33.20.Lg Ultraviolet spectra
33.20.Kf Visible spectra

Excitation spectra of neutral fragments emissions by photodissociation of OCS using VUV photons

A. Tabché‐Fouhaile@f@f, M. J. Hubin‐Franskin@f@f@f@f, J. Delwiche@f@f@f@f, H. Fröhlich@f@f, K. Ito@f@f, P. M. Guyon@f@f, and I. Nenner@f@f

J. Chem. Phys. 79, 5894 (1983); http://dx.doi.org/10.1063/1.445759 (6 pages) | Cited 12 times

Full Text: | Download PDF

Show Abstract
The Rydberg series converging to the B 2Σ+ state of OCS+ are shown to be predissociated by dissociative states leading to CS (A 1Π) and to CO triplet levels. The decay of these excited fragments is observed by their fluorescence in the visible and ultraviolet ranges. The corresponding fluorescence cross section in the 280–630 nm range is roughly estimated not to exceed 3% of the absorption. These dissociative states are very likely involved in the mechanism of resonant autoionization.
Show PACS
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.50.Dq Fluorescence and phosphorescence spectra

The ns Rydberg series of 1,3‐trans‐butadiene observed using multiphoton ionization

W. Gary Mallard, J. Houston Miller@f@f, and Kermit C. Smyth

J. Chem. Phys. 79, 5900 (1983); http://dx.doi.org/10.1063/1.445770 (6 pages) | Cited 14 times

Full Text: | Download PDF

Show Abstract
The ns Rydberg series of 1,3‐trans‐butadiene has been observed in a diffusion flame environment using two‐photon resonant multiphoton ionization in the 330–269 nm wavelength region. An analysis of the energies for the n=4 to n=12 states yields a series limit of 73 170±23 cm−1 and a quantum defect of 0.91±0.07. This ns series limit has been averaged with the limits of three other Rydberg series to give an ionization potential of 73 154±30 cm−1. The 3s and 4s states show substantial effects of mixing with the core orbitals.
Show PACS
33.20.Ni Vacuum ultraviolet spectra
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.80.Wz Other multiphoton processes

Angle‐resolved thermal and flash desorption of atoms from surfaces: Model predictions within the one‐phonon approximation

Jesus Reyes, Isidro Romero, and Frank O. Goodman

J. Chem. Phys. 79, 5906 (1983); http://dx.doi.org/10.1063/1.445771 (8 pages) | Cited 2 times

Full Text: | Download PDF

Show Abstract
We present a detailed analysis of the angular features predicted in angle‐resolved desorption, both in a steady‐state situation (thermal desorption) and in a flash desorption situation. The work is within a distorted‐wave Born approximation and a one‐phonon approximation for the atom–solid interaction. Departures from the results given by the ordinary equilibrium theory are found in all cases and are examined in terms of the following elements of our model: conservation of momentum parallel to the surface and of energy, the energy distribution of the adsorbed atoms, the phonon populations, and the matrix elements between inital and final states.
Show PACS
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Doublet→quartet and doublet→doublet electronic transitions in NO2 by electron impact@fa@f)

R. Rianda@f@f@f@f, R. P. Frueholz@f@f, and A. Kuppermann

J. Chem. Phys. 79, 5914 (1983); http://dx.doi.org/10.1063/1.445772 (4 pages) | Cited 2 times

Full Text: | Download PDF

Show Abstract
The electron‐impact energy‐loss spectrum of nitrogen dioxide (NO2) has been measured at impact energies of 25, 50, and 75 eV, and scattering angles varying from 5° to 80°. A previously unreported spin‐forbidden doublet→quartet transition was observed at 4.49 eV, in excellent agreement with theoretical calculations. Doublet→doublet transitions were observed at 2.95, 5.81, 7.48, 8.64, 9.69, 10.52, 10.68, 10.94, and 11.20 eV, in agreement with previous experimental and theoretical work. In addition, numerous doublet→doublet transitions to superexcited states were observed.
Show PACS
34.80.Gs Molecular excitation and ionization

Far infrared spectra, conformational potential function, and barrier to methyl rotation of propionyl fluoride

G. A. Guirgis@f@f, B. A. Barton, and J. R. Durig

J. Chem. Phys. 79, 5918 (1983); http://dx.doi.org/10.1063/1.445773 (9 pages) | Cited 11 times

Full Text: | Download PDF

Show Abstract
The far infrared spectra of propionyl fluoride CH3CH2CFO in the gaseous and solid states have been recorded from 500 to 40 cm−1. A rather complex spectrum of the gas was observed and a substantial number of bands have been assigned to the asymmetric torsional modes for both the s‐cis (oxygen atom eclipsing the methyl group) and the high energy gauche conformers. Analysis of these bands permitted the calculation of the torsional potential function present in this molecule. The potential coefficients for the asymmetric torsional mode were calculated to be: V1=341±24, V2=236±20, V3=390±3, and V4=21±6 cm−1, with an enthalpy difference between the more stable s‐cis and the high energy gauche conformers of 434±20 cm−1 (1.24±0.06 kcal/mol). This function gives a potential barrier of 692 cm−1 (1.98 kcal/mol) separating the s‐cis from the gauche form and 283 cm−1 (0.81 kcal/mol) separating the two equivalent gauche forms. From a temperature study of the Raman spectrum of the gas, the enthalpy difference between the s‐cis and gauche conformers was determined to be 486±45 cm−1 (1.39±0.13 kcal/mol) which is in excellent agreement with the value obtained from the potential function. The barrier to the methyl rotation for the s‐cis conformer was calculated from the far infrared data to be 935±2 cm−1 (2.67 kcal/mol). Both the methyl torsion and CFO rock were observed as doublets in the spectrum of the solid which indicates that there are at least two molecules per primitive cell. These results are compared to the corresponding quantities in some related molecules.
Show PACS
33.20.Ea Infrared spectra
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
78.30.Jw Organic compounds, polymers

A unified quantum model of resonant and direct scattering in elementary chemical reactions

Haim Shyldkrot@f@f and Moshe Shapiro

J. Chem. Phys. 79, 5927 (1983); http://dx.doi.org/10.1063/1.445774 (12 pages) | Cited 9 times

Full Text: | Download PDF

Show Abstract
A quantum model for resonant and direct exchange reactions based on Feshbach’s partitioning techniques is presented. The model is formulated in terms of the reactance matrix and hence involves only real arithmetic. Resonances are introduced via a real and symmetric effective Hamiltonian thus avoiding the search for complex eigenenergies and the construction of a bi‐orthogonal basis. The resulting equations are reduced to evaluating free–free, bound–free, and bound–bound integrals. Analytic approximations for all these integrals are developed. The model is applied to model H+OH exchange reactions and tested against exact numerical results. The well position and decelerating forces at the classical turning points are shown to determine most of the observed structure in the reactive probabilities.
Show PACS
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

Electric field effects on BZ chemical waves: Wave annihilation at negative fields

S. L. Schmidt

J. Chem. Phys. 79, 5939 (1983); http://dx.doi.org/10.1063/1.445775 (6 pages) | Cited 2 times

Full Text: | Download PDF

Show Abstract
An asymptotic solution of the Field–Körös–Noyes (FKN) model of the Belousov–Zhabotinskii (BZ) reaction is coupled with electrical conduction and thermal diffusion and the parametric dependence of the wave velocity on the electric field is analyzed. Previous theoretical and experimental evidence has verified the existence of a critical field beyond which the waves are annihilated. Furthermore, theory predicts the existence of a Fisher limiting field at which the HBrO2 front of the BZ wave has the form and velocity of a Fisher wave (velocity ≥2 in dimensionless units). In this paper theoretical evidence for a second critical field is presented. The first critical field occurs at a positive field for waves moving in the positive direction; the present result predicts a wave destruction at negative fields beyond the Fisher limiting field. These results correspond to destruction by the catalyst (at positive field) and to destruction by bromide (at negative fields).
Show PACS
82.40.Bj Oscillations, chaos, and bifurcations
Page 1 of 4 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Your Recent History Recent History Help

Recently Viewed

  1. Vibrational relaxation cross sections and rates of equilibration in electronically excited benzene (2537 Å excitation)
  2. Polymorphism of crystalline poly(hydroxymethyl) compounds. III. The structures of crystalline and plastic tris(hydroxymethyl)aminomethane
  3. Kinetics of Phase Change. I General Theory
  4. Calculated long‐range interactions and low energy scattering of Ar☒H
  5. Oscillations in chemical systems. IV. Limit cycle behavior in a model of a real chemical reaction
Go to AIP Home
Copyright © American Institute of Physics
close