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15 Jun 1986

Volume 84, Issue 12, pp. 6539-7058

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Electronic spectroscopy of tryptophan analogs in supersonic jets: 3‐Indole acetic acid, 3‐indole propionic acid, tryptamine, and N‐acetyl tryptophan ethyl ester

Young D. Park, Thomas R. Rizzo, Linda A. Peteanu, and Donald H. Levy

J. Chem. Phys. 84, 6539 (1986); http://dx.doi.org/10.1063/1.450705 (11 pages) | Cited 53 times

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The electronic spectroscopy of four different tryptophan analogs, 3‐indole acetic acid, 3‐indole propionic acid, tryptamine, and N‐acetyltryptophan ethyl ester (NATE) has been studied in a supersonic molecular beam using laser‐induced fluorescence and resonantly enhanced two‐photon ionization. The electronic transition to the lowest excited singlet state occurs at 35 039, 34 965, 34 918, and 34 881±2 cm−1 for 3‐indole acetic acid, 3‐propionic acid, tryptamine, and NATE, respectively. The relatively small differences in the electronic origin transition frequencies suggests that the lowest excited singlet state for all of these moelcules is the 1Lb state. The spectra reveal that each of these molecules have stable conformers in the gas phase, analogous to our previously reported studies of tryptophan. A low frequency vibrational mode has been observed in 3‐indole propionic acid, tryptamine, NATE, and tryptophan which involves motion of the side chain against the indole ring. We have observed that forming a van der Waals complex between tryptamine and a single methanol molecule causes the spectral features due to different conformers of the free molecule to collapse to a single line, suggesting that one particular conformer becomes the most stable species. This emphasizes the importance of including solvent interactions in any attempt to model the behavior of these molecules in solution.
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33.20.Lg Ultraviolet spectra
33.50.Dq Fluorescence and phosphorescence spectra
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Predissociation lifetimes in two excited electronic states of HCN and DCN

A. Meenakshi and K. K. Innes

J. Chem. Phys. 84, 6550 (1986); http://dx.doi.org/10.1063/1.450706 (5 pages) | Cited 13 times

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Through computer simulation of predissociated absorption bands of HCN, DCN, D13CN, and DC15N, between 54 563 and 65 644 cm−1, average linewidths and lifetimes of representative upper‐state levels are derived. Lifetimes of DC15N vary from 115 to 0.66 ps for math 1A″‐state levels. Each of the three vibrations (a′) is found to couple efficiently the math state to a second 1A″ state, allowing radiationless transitions from the math state, and subsequent dissociation. The lifetime of HCN in the zero level of the math 1A′ state is 0.95 ps, a value comparable to those of neighboring math‐state levels; therefore the dominant predissociation mechanism for the math state is assumed to be coupling of the math and math electronic states by rotation, around one or both of the in‐plane inertial axes.
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33.20.Ni Vacuum ultraviolet spectra
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.70.Fd Absolute and relative line and band intensities
33.70.Jg Line and band widths, shapes, and shifts

Second‐harmonic spectra of Fe3+ in borosilicate Pyrex glasses

I. Ciccarello, M. Guccione, and M. Li Vigni

J. Chem. Phys. 84, 6555 (1986); http://dx.doi.org/10.1063/1.450707 (5 pages)

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The second‐harmonic spectra of borosilicate Pyrex glasses containing Fe3+ impurities have been investigated at the fundamental frequency ν=2.9 GHz. The spectra are interpreted by assuming a spin‐Hamiltonian containing crystal‐field terms yielding an energy not too large in comparison to the Zeeman energy at S band. It is found that the g=4.3 second‐harmonic line does originate from the resonance of a Kramers doublet while both the g=6 line and the background signal do not. It is shown that second‐harmonic investigations allow discrimination as to whether or not a signal can be ascribed to the resonance of two spin states of the same Kramers doublet.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)

UV laser excited fluorescence spectroscopy of the jet‐cooled copper dimer

Eric A. Rohlfing and James J. Valentini

J. Chem. Phys. 84, 6560 (1986); http://dx.doi.org/10.1063/1.450708 (7 pages) | Cited 79 times

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UV laser excited fluorescence spectra of the jet‐cooled copper dimer are reported. Cu2 is produced via laser vaporization of the metal inside the throat of a pulsed, supersonic nozzle. Strong fluorescence is observed upon excitation of 63Cu2 in the range 287–324 nm, corresponding to several v″=0 bands of the II–X transition recently found in excitation using resonant two‐photon ionization [Smalley et al., J. Chem. Phys. 78, 2866 (1983)]. The II–X emission spectra are characterized by extremely long progressions in the ground state vibration, enabling us to measure G(v) and ΔGv+1/2 values over the range v=0–72. This data has been fit to yield improved vibrational constants for 63Cu2 X 1Σ+g@B: ωe =266.43±0.59 cm−1, ωexe =1.035±0.030 cm−1, ωeye =+(1.70±0.58)×10−3 cm−1, and ωeze =−(1.78±0.37)×10−5 cm−1. The G(v) data has also been fit to a near‐dissociation expansion which incorporates the correct limiting behavior of G(v), determined by the asymptotic inverse power contribution to the potential. This fit gives an improved dissociation energy for the dimer, and the vibrational index at dissociation: De =16 760±200 cm−1 and vD =128±5.
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33.50.Dq Fluorescence and phosphorescence spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Fm Bond strengths, dissociation energies

Numerical tests of a generalized multilevel vibronic coupling formalism

Y. Won, R. Lagos, and R. Friesner

J. Chem. Phys. 84, 6567 (1986); http://dx.doi.org/10.1063/1.450709 (8 pages) | Cited 4 times

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An approximate matrix continued fraction method for calculating optical line shapes of molecular systems with multilevel excited state manifolds is compared with converged basis set results. It is shown that the theory gives correct spectral envelopes for all parameter values studied.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.70.Jg Line and band widths, shapes, and shifts
31.70.Ks Molecular solids

Hyperfine structure and Λ doubling in the A 2Δ state of CH: Observation of an internal hyperfine perturbation

Wim Ubachs, W. M. van Herpen, J. J. ter Meulen, and A. Dymanus

J. Chem. Phys. 84, 6575 (1986); http://dx.doi.org/10.1063/1.450710 (6 pages) | Cited 3 times

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We report the observation of a resonance between hyperfine states, due to the crossing of rotational ladders at N=10 of Δ5/2 and Δ3/2 spin‐doublet states in the excited A 2Δ state of CH. Accurate values for the hyperfine constants a, b, and c in the A 2Δ state were obtained. From measurements of the Λ‐doublet splittings we estimate an upper limit to the Λ doubling in the A 2Δ state.
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33.15.Pw Fine and hyperfine structure
33.20.Sn Rotational analysis

Carbon spin‐lattice relaxation rate measurements during single proton excitation. A new method of internuclear distances determination

Claudio Rossi

J. Chem. Phys. 84, 6581 (1986); http://dx.doi.org/10.1063/1.450711 (3 pages) | Cited 8 times

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In this paper by combining carbon spin‐lattice relaxation rate measurements obtained under condition of broadband proton decoupling (RBB1) and single proton excitation (RSPE1) , 1H–13C internuclear distances have been determined in solution. The experimental results obtained by excitation of H6 proton of thymidine can be used to calculate proton–carbon distances in thymidine. Moreover in this paper the use of RSPE1 experimental parameter for obtaining structural and dynamical information is proposed.
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76.60.Es Relaxation effects
87.15.B- Structure of biomolecules

New parametric analysis of the optical spectra of U4+ in ThSiO4

C. Khan Malek and J. C. Krupa

J. Chem. Phys. 84, 6584 (1986); http://dx.doi.org/10.1063/1.450712 (7 pages) | Cited 19 times

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Crystals of ThSiO4–U4+ were grown by the flux method. Absorption and emission spectra were recorded from 4000 to 30 000 cm−1 at liquid helium and various higher temperatures. The transitions were assigned and fit to a semiempirical Hamiltonian with adjustable parameters via a least squares procedure. The crystal field parameters for U4+ in ThSiO4 were compared to those for U4+ in other hosts.
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78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
71.70.Ch Crystal and ligand fields
78.55.Hx Other solid inorganic materials

Frequency dependent biexponential 14N relaxation of methylisocyanide in nematic liquid crystals

L. Plomp, A. C. Loman, and J. Bulthuis

J. Chem. Phys. 84, 6591 (1986); http://dx.doi.org/10.1063/1.450851 (8 pages) | Cited 7 times

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The dynamical behavior of methylisocyanide, CH3NC, dissolved in two different nematic liquid crystals, has been studied for the first time by direct measurement of the spin‐lattice relaxation of its 14N nucleus, at three different field strengths. The results show a frequency dependent relaxation behavior, that can be described by director fluctuations in the nematic solvents. The parameters of the relaxation model: the reorientational correlation time τ⊥, and the amplitude factor A and cut‐off frequency ωc of the director fluctuation contributions, were estimated in dependence of the renormalization of the probe order parameter Sz′z. It is shown that the influence of the mean square of fluctuations 〈θ2〉 on the relaxation model can be far from negligible. Choosing literature values for the average elastic constant K and effective viscosity η in one solution (phase V), a reasonable value for the translational diffusion constant Dtr is found. The corresponding cut‐off wavelength is L∼50 Å. For the other solution (ZLI 1167), using the same L and an estimated viscosity η, reasonable values for K and Dtr are obtained. Physical arguments are used to account for the differences between the two solutions and a comparison is made with previous studies of analogous systems. It is emphasized that the value of the director fluctuation model could be enhanced by carrying out more experiments to improve the accuracy of ωc, and by refining the theoretical description of the cut‐off behavior.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
76.60.Es Relaxation effects

Raman spectrum of ferroelectric PbDPO4: Comparison with PbHPO4

N. Ohno, D. J. Lockwood, and M. H. Kuok

J. Chem. Phys. 84, 6599 (1986); http://dx.doi.org/10.1063/1.450713 (10 pages) | Cited 8 times

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The Raman spectrum of ferroelectric PbDPO4 (TC≂450 K) has been measured at temperatures between 10 and 484 K in the frequency region 8–3000 cm−1. Mode assignments have been made by comparison with similar Raman measurements on PbHPO4 (TC≂310 K). It is found that the lattice modes and PO4 internal modes are scarcely affected by the isotope change, although the high‐frequency hydrogen modes do show the expected shift to lower frequency in the deuterium compound. The overall similarities in the spectra of the two compounds both above and below TC indicate that PbDPO4 has an acentric crystal structure above TC, as was recently discovered for PbHPO4. The Raman data indicate the phase transitions in PbDPO4 and PbHPO4 are of the order–disorder type.
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78.30.Hv Other nonmetallic inorganics
77.80.-e Ferroelectricity and antiferroelectricity
64.60.Cn Order-disorder transformations

Elastic light scattering by randomly oriented macromolecules: Computation of the complete set of observables

W. M. McClain and W. A. Ghoul

J. Chem. Phys. 84, 6609 (1986); http://dx.doi.org/10.1063/1.450714 (14 pages) | Cited 27 times

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We present a calculation of all of the angle dependent observables that characterize completely the elastic scattering of light from solutions of macromolecules of arbitrary size and shape. The algorithm embodies the result of an exact analytic average over all orientations of the macromolecule, which may be large compared to the scattered wavelength. Our results are directly comparable to experiment; they are presented as a four‐by‐four Perrin matrix linking the four Stokes parameters of the incident light to the four Stokes parameters of the scattered light. The Perrin elements which we previously identified as retardation elements behave as they should: When we assume instantaneous electromagnetic interaction among the subunits of the macromolecule, they vanish; when the interaction is assumed to proceed at the speed of light, they are finite and may have easily measurable magnitude. Our algorithm captures all of the physical effects present in the Mie solution for scattering by spheres; but unlike the Mie solution it may be applied to scattering bodies of any shape, and with local variations in anisotropy.
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61.25.H- Macromolecular and polymers solutions; polymer melts
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Total absorption and photoionization cross sections of water vapor between 100 and 1000 Å

G. N. Haddad and James A. R. Samson

J. Chem. Phys. 84, 6623 (1986); http://dx.doi.org/10.1063/1.450715 (4 pages) | Cited 28 times

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Total absorption and photoionization cross sections of water vapor have been measured between 100 and 1000 Å with an accuracy of ±3%. Recent calculations are shown to be in reasonable agreement with the present data.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.20.Ni Vacuum ultraviolet spectra

Vacuum ultraviolet laser spectroscopy. IV. Spectra of Kr2 and constants of the ground and excited states

P. E. LaRocque, R. H. Lipson, P. R. Herman, and B. P. Stoicheff

J. Chem. Phys. 84, 6627 (1986); http://dx.doi.org/10.1063/1.450716 (15 pages) | Cited 62 times

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Krypton dimers formed by supersonic jet expansion have been excited with tunable, and monochromatic VUV radiation leading to isotopically resolved fluorescence excitation spectra of three band systems at 125, 124, and 117 nm. Unambiguous upper‐state vibrational numbering was possible, resulting in evaluation of the spectroscopic constants for the three lowest excited states. From system I at ∼125 nm, with bands v′=32 to 38 and v″=0, constants for the A 3Σ+u state of Kr2 were found to be T′e =74 303.9(8.0), ωe =244.60(43), ωex′e =2.6045(60), and De=5807.0(8.0) cm−1. Band system II at ∼124 nm, with bands v′=30 to 38 and v″=0, led to constants for the B 1Σ+u state, T′e =75 426.8(1.7), ωe =219.50(10), ωex′e =2.2325(15), and De =5629.1(2.5) cm−1. Improved values for constants of the C 1Σ+u state were obtained from analysis of band system III at ∼117 nm (with bands v′=0 to 5, and v″=0 to 2): T′e =85 520.60(10), ωe =43.82 (10), ωex′e =1.812(18), and De =465.3(2.0) cm−1. Vibrational constants for the ground state were obtained from bands with v″=0, 1, 2, namely ω″e =23.53(2) cm−1 and ωex″e =1.07(1) cm−1. Analyses of resolved rovibronic structure for all three band systems yielded values of rotational constants for the ground and three excited states, with the equilibrium internuclear distance r″e =4.017(12) Å for 84Kr2. These new data were used to derive potential energy curves.
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33.20.Ni Vacuum ultraviolet spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Dj Interatomic distances and angles
33.15.Fm Bond strengths, dissociation energies

The benzene ground state potential surface. I. Fundamental frequencies for the planar vibrations

Surya N. Thakur, Lionel Goodman, and Ali G. Ozkabak

J. Chem. Phys. 84, 6642 (1986); http://dx.doi.org/10.1063/1.450717 (15 pages) | Cited 56 times

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The accuracy of vapor phase vibrational data has been improved for all 12 deuterium‐labeled benzenes and for 13C12C5H6 and 13C6H6. Many vapor phase fundamental frequencies are observed for the first time. Precise isotopic frequency/splitting patterns for ν1, ν18, and ν19 have been obtained. Isotope induced harmonic mode mixing matrices are given for all 14 labeled benzenes and used to provide detailed description of the fundamental bands observed in the spectra. These descriptions provide numerous reassignments for the fundamental bands, particularily in low symmetry deuterium benzenes. The matrices show that some skeletal modes, such as ν1, gain CH stretching character as a result of deuterium labeling, providing a rationalization for the increased anharmonicity observed in recent jet experiments for C6D6. In addition, a reassessment of Fermi resonance gives 3072.3 cm−1 for the unperturbed frequency (correction +24 cm−1) for the e1u mode ν20 in C6H6 refining the CH local mode anharmonic constant, 2xii, to 117.5 cm−1.
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33.20.Ea Infrared spectra
33.20.Tp Vibrational analysis

Photoionization cross sections of rovibrational levels of the B 1Σ+u state of H2

H. Rudolph, D. L. Lynch, S. N. Dixit, and V. McKoy

J. Chem. Phys. 84, 6657 (1986); http://dx.doi.org/10.1063/1.450718 (5 pages) | Cited 11 times

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We report theoretical cross sections for direct photoionization of specific rovibrational levels of the B 1Σ+u electronic state of H2. The calculated cross sections differ considerably from values recently determined by resonant enhanced multiphoton ionization (REMPI) studies. In an attempt to understand the disagreement, we analyze in detail the REMPI dynamics and find that the multiphoton ionization probability is extremely sensitive to the spatial and temporal profiles of the laser pulses. Accurate characterization of laser profiles and their jitter is therefore necessary for a comparison between theory and experiment.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.20.Vq Vibration-rotation analysis

Laser photolysis of HNO3 at 222 nm: Direct determination of the primary quantum yield of OH

G. S. Jolly, D. L. Singleton, D. J. McKenney, and G. Paraskevopoulos

J. Chem. Phys. 84, 6662 (1986); http://dx.doi.org/10.1063/1.450719 (6 pages) | Cited 15 times

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A method has been developed and used in the direct determination of the primary quantum yield of OH in the laser photolysis of nitric acid at 222 nm. The amount of laser light absorbed was determined with a calibrated disk calorimeter. The amount of OH produced was determined by absorption spectroscopy using the resonance line at 308.3 nm and a published value of its line strength. The primary quantum yield of OH at 296 K was found to be 0.89±0.08 (95% confidence interval) with an uncertainty of +17%, −8% due to potential systematic errors. Within the experimental uncertainty, this result is consistent with a previous determination of a quantum yield of unity for the other product of photolysis, NO2.
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82.50.-m Photochemistry

Vibrational relaxation of NO (v=1) by NO, N2, CO, HCl, CO2, and N2O from 300 to 600 K

L. Doyennette and M. Margottin‐Maclou

J. Chem. Phys. 84, 6668 (1986); http://dx.doi.org/10.1063/1.450720 (11 pages) | Cited 16 times

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The vibrational relaxation of NO, laser‐excited to v=1, in collisions with NO or with other molecules, M=CO, N2, HCl, CO2, and N2O, has been studied by the laser‐induced fluorescence technique, in the temperature range from 300 to 600 K. For the NO–M systems, the relaxation occurs through competitive far‐from‐resonance V–V transfer and V–T,R deexcitation processes. Measurements of the rate constants governing the temporal decay of the fluorescence intensity emitted by the laser‐excited NO molecules were performed as a function of the molar fraction of NO. From these measurements, and those previously obtained on the same NO–M systems, but with the M molecules excited by laser, separate values, even if crude in some cases are deduced for the V–V transfer and V–T,R deexcitation rate constants. Except for NO–N2 and NO–CO, the efficiency of the V–T,R deexcitation of a molecule by collision on another one is shown to be as important as, or even greater than that of the V–V transfer from this molecule to the other one. For both NO–N2O and NO–CO2 systems, the experimental values of the V–V transfer rate constants are compared to values calculated on the basis of long‐range multipolar interactions.
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34.50.Ez Rotational and vibrational energy transfer
82.20.Rp State to state energy transfer

Reaction kinetics on ultrametric spaces

G. Zumofen, A. Blumen, and J. Klafter

J. Chem. Phys. 84, 6679 (1986); http://dx.doi.org/10.1063/1.450721 (8 pages) | Cited 20 times

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We study the kinetics of the A+A→0 and the A+B→0 diffusion‐limited reactions by modeling the dynamics through random walks on ultrametric spaces, which allow to account for energetic randomness and to incorporate effects due to changes in temperature. We treat both pseudounimolecular (target and trapping) problems, as well as bimolecular reactions, and we compare the results to those which obtain for reactions on regular lattices and on fractals. Furthermore we analyze the possibility of describing reactions on ultrametric spaces through extensions of Smoluchowski‐type approaches, and we show the limitations of such schemes when, as a function of temperature and of the reaction progress, the fluctuations in the particle densities get large.
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82.20.Wt Computational modeling; simulation
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
66.30.-h Diffusion in solids

Quenching of I∗(5 2P1/2) by halogen fluorides

M. A. Chowdhury, A. T. Pritt, D. Patel, and D. J. Benard

J. Chem. Phys. 84, 6687 (1986); http://dx.doi.org/10.1063/1.450722 (7 pages) | Cited 6 times

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Absolute rate constants of the collisional decay of I(5 2P1/2) by the halogen fluorides F2, ClF, and IF have been determined using the technique of time‐resolved, laser‐initiated infrared fluorescence, as well as atomic absorption spectroscopy (in the case of IF only). The room temperature rate constants, kF2<8.7×10−14, kCIF=1.3±0.3×10−13, and kIF (∼400 K) =1.3±0.6×10−11 cm3 molecule−1 s−1, along with other reported quenching rate constants for the other halogen diatomics have been explained in terms of correlations based on the symmetry of the relevant potential energy surfaces.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
32.50.+d Fluorescence, phosphorescence (including quenching)

Electronic quenching of I2 B 3Π(0+u) by He at low collision energies

Jean‐Philippe Nicolai and Michael C. Heaven

J. Chem. Phys. 84, 6694 (1986); http://dx.doi.org/10.1063/1.450723 (5 pages) | Cited 6 times

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Electronic quenching of I2 B 3Π(0+u), v′=11 by He has been investigated in a free jet expansion. The quenching cross section was found to be 0.33±0.08 Å2 at 9.4 K, which is significantly smaller than the room temperature value (0.89±0.02 Å2). The temperature dependence of the cross section has been quantitatively characterized in terms of a collision induced predissociation model. Calculations based on this model show that the predissociation is induced by dispersion forces acting between the collision partners, and they provide information about the symmetry of the repulsive state involved. The calculations are also shown to be compatible with the predissociation and fluorescence decay dynamics of the HeI2 (B) van der Waals complex.
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34.50.Gb Electronic excitation and ionization of molecules
33.50.Hv Radiationless transitions, quenching
33.50.Dq Fluorescence and phosphorescence spectra

Three‐dimensional analytical model for the photodissociation of symmetric triatomics. Absorption and fluorescence spectra of ozone

O. Atabek, M. T. Bourgeois, and M. Jacon

J. Chem. Phys. 84, 6699 (1986); http://dx.doi.org/10.1063/1.450724 (13 pages) | Cited 32 times

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A full three‐dimensional analytical Franck–Condon analysis is presented for dissociative spectroscopies of a symmetric triatomic system. Formulas derived for harmonic potential surfaces are applied to the theoretical calculation of ozone absorption spectrum in the Hartley continuum as well as to the determination of its fluorescence (or resonance Raman) spectrum when submitted to 266 nm wavelength excitation. The Hartley absorption line shape describing the 1 1B2←X 1A1 photodissociation is reproduced within very good agreement with experiment. The role of the so‐called Duschinsky effect originating from the coupling of bending and stretching motions in the excited state is analyzed and comparisons are presented with previous more simple models neglecting this coupling. The influence of temperature is also taken into account through calculations dealing with vibrationally excited species. As for the photoemission fluorescence spectrum carrying a rich information content, the behavior is successfully predicted in its main lines, relative intensities of overtone progressions and of combination bands are fairly well reproduced.
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33.20.Lg Ultraviolet spectra
33.80.Gj Diffuse spectra; predissociation, photodissociation
82.33.Tb Atmospheric chemistry
82.50.Hp Processes caused by visible and UV light

Tests of the extension of variational transition state theory to calculate reaction rates for molecules in selected excited vibrational states

Rozeanne Steckler, Donald G. Truhlar, and Bruce C. Garrett

J. Chem. Phys. 84, 6712 (1986); http://dx.doi.org/10.1063/1.450673 (7 pages) | Cited 10 times

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Variational transition state theory (VTST) with an adiabatic approximation for excited vibrational modes and semiclassical transmission coefficients to account for tunneling is used to calculate state‐specific reaction rates for the collinear reaction H+F2(n=1)→HF+H and the three‐dimensional reaction Cl+H2(n=1–4,7)→HCl+H, where n is the initial vibrational quantum number and the rate constants are summed over final vibrational states. We also consider deuterated and tritiated analogs for both reactions for n=1. The results are compared to previous state‐selected rate constants calculated without transition state assumptions. Comparisons to accurate quantal results for the H+F2 series test both the semiclassical tunneling methods and the validity of the adiabatic approximation for excited‐state dynamical‐bottleneck locations. Comparison to quasiclassical trajectory calculations for the Cl+H2 series provide further tests of the adiabatic approximation. In general the VTST/adiabatic‐plus‐tunneling calculations are quite successful.
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82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Rp State to state energy transfer
82.20.Db Transition state theory and statistical theories of rate constants

Potential energy curves for the a 3Σu+ and c 3Σ+g states of He2 consistent with differential scattering, ab initio theory, and low‐temperature exchange rates

R. M. Jordan, H. R. Siddiqui, and P. E. Siska

J. Chem. Phys. 84, 6719 (1986); http://dx.doi.org/10.1063/1.450674 (9 pages) | Cited 24 times

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Crossed beam scattering experiments on He∗(2 3S)+He at energies of 0.94, 1.51, and 2.24 kcal/mol have been combined with ab initio theory and kinetic data on metastability exchange rates to produce new estimates of the title potential energy curves. The long‐range potential barrier in the a state is found to be 1.43±0.05 kcal/mol at a separation of 2.717±0.04 A. Combining these results with those for the corresponding singlet states from an earlier paper [J. Chem. Phys. 80, 5027 (1984)], we discuss the long‐range behavior of the curves, particularly with respect to curve crossing between a given pair of g and u states. These crossings, which conform to theoretical predictions, appear to be essential for a consistent description of all available data.
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34.50.Lf Chemical reactions
34.20.Cf Interatomic potentials and forces

Dissociative attachment reactions of electrons with strong acid molecules

Nigel G. Adams, David Smith, A. A. Viggiano, John F. Paulson, and Michael J. Henchman

J. Chem. Phys. 84, 6728 (1986); http://dx.doi.org/10.1063/1.450675 (4 pages) | Cited 19 times

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Using the flowing afterglow/Langmuir probe (FALP) technique, we have determined (at variously 300 and 570 K) the dissociative attachment coefficients β for the reactions of electrons with the common acids HNO3 (producing NO−2) and H2SO4 (HSO−4), the superacids FSO3H (FSO−3), CF3SO3H (CF3SO−3), ClSO3H (ClSO−3,Cl−), the acid anhydride (CF3SO2)2O (CF3SO−3), and the halogen halides HBr (Br−) and HI (I−). The anions formed in the reactions are those given in the parentheses. The reactions with HF and HCl were investigated, but did not occur at a measurable rate since they are very endothermic. Dissociative attachment is rapid for the common acids, the superacids, and the anhydride, the measured β being appreciable fractions of the theoretical maximum β for such reactions, βmax. The HI reaction is very fast ( β∼βmax) but the HBr reaction occurs much more slowly because it is significantly endothermic. The data indicate that the extreme acidity of the (Bronsted‐type) superacids has its equivalence in the very efficient gas‐phase dissociative attachment which these species undergo when reacting with free electrons. The anions of the superacids generated in these reactions, notably FSO−3 and CF3SO−3, are very stable (unreactive) implying exceptionally large electron affinities for the FSO3 and CF3SO3 radicals.
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
34.80.Gs Molecular excitation and ionization

Two‐photon ionization of atomic systems treated by means of the complex coordinate method

P. Froelich and A. Flores‐Riveros

J. Chem. Phys. 84, 6732 (1986); http://dx.doi.org/10.1063/1.450676 (6 pages) | Cited 5 times

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A L2 discretization of the continuum within the scope of the complex coordinate technique is employed to obtain the differential cross section for two‐photon ionization of atomic systems. The method avoids explicit construction of the continuum final state and instead dispersion relations are utilized to evaluate the appropriate transition matrix element controlling the process, to second order of perturbation theory in the nonrelativistic dipole approximation. The method is applied to the two‐photon ionization of atomic hydrogen.
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32.80.Rm Multiphoton ionization and excitation to highly excited states
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