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15 Jun 1984

Volume 80, Issue 12, pp. 5883-6331

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Complete determination of the state multipoles of rotationally resolved polarized fluorescence using a single experimental geometry

A. J. Bain and A. J. McCaffery

J. Chem. Phys. 80, 5883 (1984); http://dx.doi.org/10.1063/1.446692 (10 pages) | Cited 23 times

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When laser radiation is used to prepare single rovibronic levels in molecules, the excited state Mj distribution is invariably polarized. In many such experiments the polarization of the excited state is ignored, which is an inadequate basis for accurate work as much valuable detail is lost. A better approach is a completely polarization resolved experiment in which the preparation, dynamics, and detection of the excited state polarization components (the state multipoles JJρKQ) are fully described. A treatment of polarized excitation in terms of the state multipoles JJρKQ is presented and consideration of excited state symmetry indicates that a common experimental geometry for linearly and circularly polarized excitation is feasible. A complete determination of the state multipoles (K=0,1,2) is shown to be possible within a single experimental geometry. It is shown that neglect of polarization phenomena can lead to ambiguities in the interpretation of some experiments.
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33.50.Dq Fluorescence and phosphorescence spectra
31.50.Df Potential energy surfaces for excited electronic states
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

CO2 and CO laser microwave double resonance spectroscopy of OCS: Precise measurement of dipole moment and polarizability anisotropy

Keiichi Tanaka, Hajime Ito, Kensuke Harada, and Takehiko Tanaka

J. Chem. Phys. 80, 5893 (1984); http://dx.doi.org/10.1063/1.446693 (13 pages) | Cited 38 times

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Laser–microwave double resonance (LMDR) with high electric field was applied to the OCS molecule. Stark Lamb‐dip spectra due to the infrared transitions of the 2ν2(0200–0000, 9.6 μm), 2ν1 (2000–0000, 5.8 μm), and ν1+2ν2 (1200–0000, 5.3 μm) bands were observed with the CO2 and CO lasers. The spectra due to the corresponding hot bands; 0310–0110, 0400–0200, 1200–1000, 1310–1110; 2110–0110, 3000–1000; 1400–0200, 1420–0220, 1510–0310, 2200–1000; and a few bands of OC34S and O13CS were also identified. Associated with these infrared transitions, more than 90 LMDR signals were detected and assigned to rotational transitions in the 11 vibrational states 0000, 1000, 2000, 0110, 0200, 0220, 0310, 0400, 1200, 1420, and 2200 of the normal species, and in the two vibrational states 0000 and 0200 of both OC34S and O13CS. Dipole moments were determined with accuracies (2.5σ) better than 2×10−5 D for all these vibrational states. Polarizability anisotropies were also obtained for some states. The data for the ground ν1 and ν2 vibrational states are, with the 2.5σ uncertainties in parentheses.From the Stark Lamb‐dip spectra the origins of various vibrational bands were determined, among which those for the 0200–0000 and 0310–0110 bands are 31 389 530.4(25) and 31 566 477.57(67) MHz, respectively. The dipole moments and band origins obtained in the present study agree well with the available accurate values from molecular beam electric resonance and heterodyne measurement, respectively. A procedure for the calibration of electric field in laser Stark and double resonance spectroscopy, in which the dipole moment of OCS is used as the standard, is described.
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33.40.+f Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance)
33.20.Bx Radio-frequency and microwave spectra
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Visible and near IR Si–H vibrational overtones in SiH4

R. A. Bernheim, F. W. Lampe, J. F. O’Keefe, and J. R. Qualey

J. Chem. Phys. 80, 5906 (1984); http://dx.doi.org/10.1063/1.446694 (3 pages) | Cited 14 times

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Absorption spectra in the 12 000 to 18 000 cm−1 range have been recorded for gaseous SiH4 using intracavity photoacoustic detection with cw dye lasers. The observed transitions correspond to the Δv=6–9 overtones of the Si–H local mode stretch and show considerable rotational structure.
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33.20.Ea Infrared spectra
33.20.Kf Visible spectra

A spectroscopic study of the F(0+u) ion‐pair state of Br2 by the double resonance method

Tsutomu Shinzawa, Atsuto Tokunaga, Takashi Ishiwata, Ikuzo Tanaka, Kazuo Kasatani, Masahiro Kawasaki, and Hiroyasu Sato

J. Chem. Phys. 80, 5909 (1984); http://dx.doi.org/10.1063/1.446695 (7 pages) | Cited 12 times

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A new ion‐pair state of Br2 has been observed by an optical–optical double resonance technique utilizing ultraviolet fluorescence detection. The OODR excitations proceed in an one‐photon resonant three‐photon absorption through the B3Π (0+u) state. The effects of polarization on their transition strengths are used to determine the symmetry of excited molecular state formed by two‐photon absorption from the B state. The results indicate that the new state has the 0+u symmetry with Te=53 899.6(7) cm−1, ωe=155.8(2) cm−1, and re=3.276(8) Å for 79Br2. This state is expected to correlate with Br+(3P0)+Br−(1S) and named F (0+u) after the well‐defined I2 molecule. The single rovibronic fluorescence spectra of the F(0+u) state show several transitions terminating on low‐lying valence states.
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33.40.+f Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance)
33.50.Dq Fluorescence and phosphorescence spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

ENDOR of benzil in bibenzyl: The dominance of crystal forces

I. Y. Chan and C. J. Sandroff

J. Chem. Phys. 80, 5916 (1984); http://dx.doi.org/10.1063/1.446696 (6 pages) | Cited 1 time

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A proton ENDOR investigation has been conducted on the lowest triplet state of benzil in bibenzyl. The triplet molecule was shown to possess a precise center of inversion. The dicarbonyl fragment therefore has to be precisely trans‐planar. The orientation of the two phenyl rings with respect to the dicarbonyl plane was semiquantitatively determined. These results, in comparison with a previous study on the geometry of triplet benzil in its own lattice, demonstrate the dominant role of lattice packing on determining the conformation and spectroscopy of flexible chromophores.
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76.70.Dx Electron-nuclear double resonance (ENDOR), electron double resonance (ELDOR)

Microwave spectrum and internal rotation of 2‐butyne‐1, 1, 1‐d3 (dimethylacetylene), CH3C≡CCD3

Jun Nakagawa, Michiro Hayashi, Yasuki Endo, Shuji Saito, and Eizi Hirota

J. Chem. Phys. 80, 5922 (1984); http://dx.doi.org/10.1063/1.446697 (4 pages) | Cited 4 times

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The rotational transitions of CH3C≡CCD3 have been observed for J=13←12, 15←14, 18←17, 19←18, 20←19, 22←21, 23←22, and 26←25 using a source‐frequency modulation microwave spectrometer with a 3.7 m long free space absorption cell maintained at −50 to −60 °C. The observed spectrum clearly shows the effect of internal rotation with a small potential barrier. The expression for the rotational transition frequency derived by Kirchhoff and Lide [J. Chem. Phys. 43, 2303 (1965)] using a second‐order perturbation theory for the contributions of the internal rotation was employed in analyzing the observed spectrum, and the least‐squares analysis has yielded the rotational constant B=2982.4980±0.0011 MHz and a few centrifugal distortion constants. The barrier height to internal rotation has been estimated to be 5.62±0.16 cm−1.
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33.20.Bx Radio-frequency and microwave spectra
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

The b 1Σ+ → X 3Σ− transition in PH: A measurement of the term energy, bond length, and vibrational frequency of a phosphinidene metastable

A. T. Droege and P. C. Engelking

J. Chem. Phys. 80, 5926 (1984); http://dx.doi.org/10.1063/1.446698 (4 pages) | Cited 8 times

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The (0,0), (1,1), and (2,2) vibrational bands of the weak, spin forbidden b 1Σ+ → X 3Σ− transition of the PH radical have been observed in a flowing afterglow of PH3 in He. The spectra yield the following constants for the upper b state: Te =(14 325.5±0.1) cm−1, Be =(8.587±0.003) cm−1, we =(2403.0±0.1) cm−1, Dv =(4.0±0.05×10−4) cm−1, αe =(0.0253±0.003) cm−1, and re =(1.4178±0.0004) Å. The intensity distribution is consistent with the mixing of the b 1Σ+ state almost exclusively with the A 3Π state.
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33.20.Kf Visible spectra
33.20.Lg Ultraviolet spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

A Raman study of matrix isolated methane

E. Regitz, A. Loewenschuss, K. D. Bier, and H. J. Jodl

J. Chem. Phys. 80, 5930 (1984); http://dx.doi.org/10.1063/1.446699 (7 pages) | Cited 4 times

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The Raman spectrum of methane in solid matrices is reported. The ν1 and ν3 modes were observed in argon, krypton, xenon, and nitrogen matrices, and the effect of temperature and concentration changes investigated. The ν2 transition was recorded in Ar, Kr, and Xe solids. For CD4 the ν1, ν2, 2ν2, and ν3 bands were measured in xenon matrices. The rotational band structure observed in the ν3 and ν2 modes is related to a theoretical model for matrix isolated methane, existing for ν3 and applied by us to ν2 also, and to the free molecular transitions. Our results are compared to previously published Raman spectra and differences and discrepancies are pointed out.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)

Pressure‐induced splitting and collapsing of the CN stretching vibration band in the Raman spectrum of crystalline Hg(CN)2

P. T. T. Wong

J. Chem. Phys. 80, 5937 (1984); http://dx.doi.org/10.1063/1.446673 (5 pages) | Cited 4 times

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Raman spectra of crystalline Hg(CN)2 have been measured as a function of pressure up to 45.1 kbar. The CN stretching band appears as a singlet in the pressure range 0–16 kbar and its frequency exhibits a nonlinear pressure dependence. It becomes a doublet and shifts to lower frequency at 20 kbar where a structural phase transition takes place. The intensity of the high‐frequency component of the doublet decreases with increasing pressure and totally disappears at 40 kbar where a second structural phase transition takes place. The phase transition at 20 kbar is driven by the intramolecular distortion and the intermolecular coordination processes and the transition at 40 kbar is triggered by an increase of symmetry of the molecular configuration.
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78.30.Hv Other nonmetallic inorganics
62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions

Optical and magnetic properties of uranium borohydride and tetrakismethylborohydride

K. Rajnak, E. Gamp, R. Shinomoto, and N. Edelstein

J. Chem. Phys. 80, 5942 (1984); http://dx.doi.org/10.1063/1.446674 (9 pages) | Cited 8 times

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The U(BD4)4/Hf(BD4)4 optical spectrum reported by Bernstein and Keiderling has been reanalyzed. All 19 allowed transitions have been identified. The crystal field is ∼2.5 times as strong as that of  U4+/ThBr4, but the values of the Fk and ζ parameters are nearly the same. The magnetic susceptibility of the structurally related molecule U(BH3CH3)4 has been measured from 2–330 K. Using the eigenvectors from the optical analysis, the magnetic data can be fit with an orbital reduction factor k=0.85. For U(BD4)4/Hf(BD4)4 k=ζ/ζfree ion=0.91.
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78.40.Ha Other nonmetallic inorganics
71.70.Ch Crystal and ligand fields
75.20.Ck Nonmetals
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Analysis of the optical spectrum of Np(BD4)4 diluted in Zr(BD4)4 and the magnetic properties of Np(BH4)4 and Np(BH3CH3)4

K. Rajnak, R. H. Banks, E. Gamp, and N. Edelstein

J. Chem. Phys. 80, 5951 (1984); http://dx.doi.org/10.1063/1.446675 (12 pages) | Cited 10 times

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The optical spectrum of Np(BD4)4/Zr(BD4)4 is reported and analyzed. The parameter values obtained are consistent with those for U(BD4)4/Hf(BD4)4. A total of 46 levels were fit with σ=84 cm−1. EPR data on Np(BD4)4/Zr(BD4)4 and Np(BH3CH3)4/Zr(BH3CH3)4 and the magnetic susceptibility of Np(BH3CH3)4 are reported. They could be fit with the eigenvectors from the optical analysis only by the inclusion of orbital reduction factors k=0.885 for Np(BD4)4 and 0.862 for Np(BH3CH3)4. These values indicate greater covalency for the methylborohydride.
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78.40.Ha Other nonmetallic inorganics
76.30.-v Electron paramagnetic resonance and relaxation
75.20.Ck Nonmetals
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Effects of small distortions on the EPR of the Γ6 state (Td symmetry) of Np(BH3CH3)4 diluted in Zr(BH3CH3)4

E. Gamp and N. Edelstein

J. Chem. Phys. 80, 5963 (1984); http://dx.doi.org/10.1063/1.446676 (5 pages) | Cited 3 times

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The single crystal and powder EPR spectra of 237Np(BH3CH3)4 diluted in Zr(BH3CH3)4 are reported and interpreted in terms of an orthorhombic spin Hamiltonian with gx=1.7739(4), gy=1.8292(4), gz=1.7961(5), Ax=0.1079(2) cm−1, Ay=0.1153(2) cm−1, Az=0.1135(2) cm−1. A modified point charge calculation indicates qualitatively that very small deviations of the site symmetry from Td are enough to account for the observed splitting of the g values.
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76.30.-v Electron paramagnetic resonance and relaxation

Stimulated emission spectroscopy: A complete set of vibrational constants for math 1A1 formaldehyde

David E. Reisner, Robert W. Field, James L. Kinsey, and Hai‐Lung Dai

J. Chem. Phys. 80, 5968 (1984); http://dx.doi.org/10.1063/1.446677 (11 pages) | Cited 111 times

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A complete set of 27 normal mode vibrational constants ω0i and xi j as well as six harmonized vibrational frequencies ωi is obtained for the H2CO math1A1 state: ω01 =2811.42(15), ω02 =1755.858(40), ω03 =1500.32(49), ω04 =1170.224(30), ω05 =2861.30(14), ω06 =1250.565(63) x11=−28.95(14), x12=1.15(19), x13=−23.03(14), x14=−10.099(65), x15=−193.32(24), x16=−49.78(33) x22=−9.926(23), x23=−8.26(11), x24=−7.199(39), x25=−17.23(23), x26=6.581(49), x33=−0.164(97), x34=−1.769(52), x35=6.00(37), x36=−29.861(88), x44=−3.157(12), x45=−13.35(17), x46=−2.860(70) x55=−17.97(13), x56=−17.63(33), x66=−1.567(56), ω1=2977.91(31), ω2=1778.26(16), ω3=1528.95(54), ω4=1191.02(11), ω5=2997.04(36), ω6=1298.91(26) (1σ uncertainty in parentheses). These vibrational constants are derived primarily from stimulated emission pumping (SEP) spectra of more than 50 4500–9300 cm−1 vibrational levels of the math1A1 state, supplemented by partial rotational analyses of 12 4000–8100 cm−1 FTIR overtone and combination bands. This is the first time that the SEP technique has been systematically applied to a traditional but seldom achievable objective of high resolution vibrational spectroscopy, determination of a complete set of ω0i and xi j constants. Insofar as the rotationless vibrational levels of H2CO math1A1 can each be unambiguously assigned a set of normal mode quantum numbers and reproduced by a minimal set of vibrational constants, the math state of formaldehyde remains vibrationally well organized up to at least 9300 cm−1.
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33.40.+f Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance)
33.20.Tp Vibrational analysis
33.20.Ea Infrared spectra

Intermolecular vibrations of two 1:1 complexes between CH3CN and HCN in solid Ar

Erich Knözinger and Rüdiger Wittenbeck

J. Chem. Phys. 80, 5979 (1984); http://dx.doi.org/10.1063/1.446678 (4 pages) | Cited 4 times

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The far IR spectra of mixtures of acetonitrile and hydrogen cyanide isolated in solid argon have been measured over the range 200–10 cm−1. Depending on the physical conditions and on the sample preparation, absorption patterns of two different 1:1 complexes have been observed: (a) a predominantly antiparallel structure giving rise to four far IR bands and (b) a more stable linear hydrogen bonded structure exhibiting only two far IR bands.
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33.20.Ea Infrared spectra

Far infrared and low frequency gas phase Raman spectra and conformational stability of the 1‐halopropanes

J. R. Durig, S. E. Godbey, and J. F. Sullivan

J. Chem. Phys. 80, 5983 (1984); http://dx.doi.org/10.1063/1.446679 (11 pages) | Cited 19 times

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The far infrared (375–50 cm−1) and low frequency Raman (400–70 cm−1) spectra of the gaseous 1‐halopropanes CH3CH2CH2F, CH3CH2CH2Cl, and CH3CH2CH2Br have been recorded and both the methyl and asymmetric torsional modes have been observed and assigned for both the gauche and trans conformers for all of these molecules. The asymmetric torsions for each molecule have several observed excited states which fall on the low frequency side of the fundamental. The asymmetric torsional potential functions have been calculated and, from these potential functions, the enthalpy differences between the high energy trans and low energy gauche conformers have been determined to be 122±10 cm−1 for the fluoride, 127±10 cm−1 for the chloride, and 37±10 cm−1 for the bromide. The trans and gauche methyl torsions have also been observed and assigned for the three 1‐halopropanes. The resulting barriers in cm−1 are: 936±4 (trans), 986±9 (gauche) for 1‐fluoropropane; 929±2 (trans), 1080±3 (gauche) for 1‐chloropropane; and 841 (trans), 1016±8 (gauche) for 1‐bromopropane. A complete vibrational assignment has also been made for the 1‐fluoropropane molecule and, from the spectral data for the solid, it appears that there are two or more molecules per primitive cell. Attempts to obtain experimental values for the enthalpy differences in the gas phase were made and these results, as well as the determined potential functions, are discussed in relation to previous studies.
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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)

Cold jet infrared absorption spectroscopy: The ν3 band of WF6

Michio Takami and Hiroaki Kuze

J. Chem. Phys. 80, 5994 (1984); http://dx.doi.org/10.1063/1.446680 (5 pages) | Cited 12 times

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The ν3 band of WF6 is studied at a low rotational and vibrational temperature by using a tunable diode laser. Infrared absorption in a pulsed supersonic free jet of WF6 is observed by phase sensitive detection synchronized with the pulse frequency. Absorption lines of four isotopic species, 182WF6, 183WF6, 184WF6, and 186WF6 are measured between 711.5 and 716.6 cm−1 with a Doppler limit resolution. Five molecular constants, ν3, B3, Bζ3, F110, and α224 are determined for each isotopic species and α220 for 186WF6. Isotope shift for the ν3 band is determined to be −0.316 cm−1/amu.
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33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

Strong vibronic coupling in molecular Rydberg states

Robert L. Whetten and Edward R. Grant

J. Chem. Phys. 80, 5999 (1984); http://dx.doi.org/10.1063/1.446681 (7 pages) | Cited 22 times

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We consider the vibronic properties of molecular Rydberg states in the strong coupling (degenerate) limit of the ion core, and show how the observed optical Rydberg spectrum for such a molecule is closely related to the Franck–Condon spectrum of its Jahn–Teller ion core, regardless of the symmetry labels attached to the Rydberg electronic species. These relationships permit the resolution of a quarter‐century old paradox in the Rydberg spectrum of benzene and give rise to easily verifiable predictions concerning benzene’s vibronic spectrum, which are applied to a recently discovered new Rydberg series. We further suggest that observed deviations from the idealized Rydberg case discussed here will reveal additional details about the coupling of Rydberg electronic and core‐vibronic motion.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.20.Ni Vacuum ultraviolet spectra

Photoassociative laser‐induced fluorescence of XeCl∗ and kinetics of XeCl(B) and XeCl(C) in Xe

Gen Inoue, J. K. Ku, and D. W. Setser

J. Chem. Phys. 80, 6006 (1984); http://dx.doi.org/10.1063/1.446682 (14 pages) | Cited 51 times

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Laser induced fluorescence studies have been done with XeCl molecules, which demonstrate photoassociation (free–bound absorption) as well as conventional bound–bound absorption from the XeCl(X) van der Waals molecules. The XeCl(X) and Xe+Cl pairs were generated by a pulsed dc discharge through 1–6 Torr Xe/Cl2 mixtures. Experiments also were done with Xe/HCl mixtures. The time and wavelength resolved XeCl(B–X) and XeCl(C–A) excitation and fluorescence spectra are reported. Model calculations were done to demonstrate that the laser excitation spectra for XeCl(B,v=0−3) show laser‐assisted photoassociation. The time resolved decay of the XeCl(B,v′=0) and XeCl(C,v′=0,1) states was used to measure the radiative lifetimes 11.1±0.2 and 131±10 ns, respectively, and the XeCl(B) and XeCl(C) coupling and quenching rate constants. The transfer and quenching rate constants for XeCl(B) by Xe are assigned as (11±1)×10−11 and (2.3±0.3)×10−11 cm3 molecule−1 s−1, respectively; although, the sum is known with greater certainty than the individual values. The quenching rate constants of XeCl(B,v′=0) by Cl2 and HCl are (4.3±0.2)×10−10 and (6.3±0.5)×10−10 cm3 molecule−1 s−1. Evidence is presented to show that the B–C coupling rate constants are comparable to the XeCl(B,C) vibrational relaxation rate constants for XeCl(B,v′=2) in collisions with Xe.
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82.50.Hp Processes caused by visible and UV light
82.20.Rp State to state energy transfer
33.50.Dq Fluorescence and phosphorescence spectra

The excited states of 1, 3‐butadiyne determined by electron energy loss spectroscopy

Michael Allan

J. Chem. Phys. 80, 6020 (1984); http://dx.doi.org/10.1063/1.446683 (5 pages) | Cited 11 times

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Dipole forbidden electronic transitions in butadiyne were studied in the range 2–12 eV using a trochoidal electron spectrometer. The lowest observed feature is weak, structureless, with an onset sround 2.7 eV, and is probably due to the lowest excited state 3Σ+u . The second triplet state 3Δu is observed at 3.216 ±0.01 eV(000), respectively 4.2±0.2 eV (vertical). It exhibits long progressions in the ν′2 C≡C stretch and ν6 C–H bend vibrations. The latter indicates a bent equilibrium configuration. The UV inactive 000 transition of the 1Δu state is observed at 5.06±0.01 eV with low electron energies. This value is in excellent agreement with the prediction of Jungen et al. based on the interpretation of the UV absorption. At higher electron energies only the UV active vibronic transitions of this state are observed. With low electron energies a number of narrow bands corresponding to dipole forbidden transitions are observed above 7 eV. They are tentatively grouped into three new Rydberg series with δ=0.46, 0.5, and 0.87. Finally, three narrow anion states (Feshbach resonances) are observed at 6.71, 6.82, and 7.00±0.04 eV. They decay preferentially by emission of a slow (≤0.3 eV) electron.
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34.80.Gs Molecular excitation and ionization
31.50.Df Potential energy surfaces for excited electronic states

Collisional dissociation and chemical relaxation of alkali halide molecules: 2000–4200 K

Richard Milstein and R. Stephen Berry

J. Chem. Phys. 80, 6025 (1984); http://dx.doi.org/10.1063/1.446684 (13 pages) | Cited 1 time

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Shock‐induced dissociation and the subsequent chemical relaxation processes of diatomic alkali halide molecules have been studied by time‐resolved absorption spectrometry of alkali atoms, halide ions, and alkali halide molecules. The salts studied in detail are NaCl, KBr, RbCl, RbBr, CsCl, CsBr, and CsI. Rate coefficients have been determined in the temperature range2000–4200 K for these processes: collisional detachment by argon Ar+X−→Ar+X+e; ionization of alkali atoms by thermal electron impact e+M0→2e+M+; ion–ion neutralization M++X−→M0+X0; collisional dissociation to ions Ar+MX→Ar+M++X−; and finally, collisional dissociation to atoms Ar+MX→Ar+M0+X0. The branching ratio (probability of dissociation to atoms)/(probability of dissociation to ions) is, in all cases studied, favorable to formation of ion pairs, relative to the equilibrium distribution of atom pairs/ion pairs. However, in every case except CsI, the primary collisional dissociation process gives a significant fraction of atom pairs.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Pm Rate constants, reaction cross sections, and activation energies

Scaling of state multipoles in rotationally inelastic transfer

M. J. Proctor and A. J. McCaffery

J. Chem. Phys. 80, 6038 (1984); http://dx.doi.org/10.1063/1.446685 (9 pages) | Cited 1 time

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Laser excitation of molecules in thermal cells gives rise to an anisotropic distribution of m states and thus fluorescence from these states, and from levels populated by inelastic collisions, is polarized. Neglect of fluorescence polarization can give rise to misleading conclusions concerning population transfer in the excited state. Precise measurements of the transfer of population, orientation, and alignment, through polarization ratios, can provide an excellent means for testing the various fitting laws for rotationally inelastic transfer through modified ‘‘sudden’’ scaling laws. The justification for this is fourfold: rotational line strength factors and laser power fluctuations do not affect the degree of polarization; thirdly, the effect of multiple collisions is less significant on the inelastic polarization transfer than it is on the population transfer as measured in conventional total fluorescence intensity measurements; and fourthly, the leading parameters present in fitting laws cancel out, reducing the number of fitting parameters by one. Scaling laws appropriate to polarization measurements are derived and various fitting relations are tested against Li@B|2/He and Li∗2/Ar rotationally inelastic polarization data.
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34.50.Ez Rotational and vibrational energy transfer
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
31.50.Df Potential energy surfaces for excited electronic states
33.50.Dq Fluorescence and phosphorescence spectra

New aspects of the ‘‘channel three’’ problem in benzene, as revealed by multiphoton ionization photoelectron spectroscopy

Yohji Achiba, Atsunari Hiraya, and Katsumi Kimura

J. Chem. Phys. 80, 6047 (1984); http://dx.doi.org/10.1063/1.446686 (5 pages) | Cited 24 times

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Combining a photoelectron spectroscopic technique with a (1+1) resonant ionization method, we have investigated intramolecular decay processes of benzene in its S1 state under collision‐free conditions. Photoelectron spectra were obtained by selective excitation of benzene with a pulsed UV laser at several single vibronic levels of the S1 state up to an internal energy (ΔE) of 5000 cm−1. These spectra strongly suggest that the excitation of benzene at the vibronic bands above the onset of the ‘‘channel three’’ is followed by intramolecular vibrational redistribution within the S1 state. It is concluded that there are no decay channels faster than this redistribution process up to ΔE=5000 cm−1 at the first decay stage. The results of the integrated multiphoton ionization intensity distribution over the vibronic bands, as well as the internal‐energy dependent spectral changes observed in the photoelectron spectra, also strongly suggest that the channel three is initiated by the redistributed vibrational modes, which lead to a fast internal conversion leads to the ground electronic state.
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33.60.+q Photoelectron spectra
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.80.Wz Other multiphoton processes
33.80.Eh Autoionization, photoionization, and photodetachment

On the mechanism of the CO self‐exchange reaction

A. Rockwood, D. L. Bahler, and E. A. McCullough

J. Chem. Phys. 80, 6052 (1984); http://dx.doi.org/10.1063/1.446687 (10 pages)

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The gas phase exchange reaction with stoichiometry 13C 16O+12C 18O→13C 18O+12C 16O has been studied using a mercury photosensitization technique. The mechanism of the photosensitized exchange reaction is complex and almost certainly involves electronically excited CO(a 3Π). No evidence for a simple bimolecular exchange mechanism involving ground electronic state, vibrationally excited CO was found, although such a mechanism is not conclusively ruled out by the photosensitization experiments for vibrational levels higher than 9. Since such a mechanism has previously been proposed based on shock tube studies, a computer simulation of the shock tube exchange reaction was undertaken. One set of shock tube experiments can be reinterpreted quite well in terms of an atomic chain mechanism initiated by traces of O2 impurity. The mechanism of the second set remains a mystery.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Wt Computational modeling; simulation

Explodator: A new skeleton mechanism for the halate driven chemical oscillators

Z. Noszticzius, H. Farkas, and Z. A. Schelly

J. Chem. Phys. 80, 6062 (1984); http://dx.doi.org/10.1063/1.446688 (9 pages) | Cited 19 times

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In the first part of this work, some shortcomings in the present theories of the Belousov–Zhabotinskii oscillating reaction are discussed. In the second part, a new oscillatory scheme, the limited Explodator, is proposed as an alternative skeleton mechanism. This model contains an always unstable three‐variable Lotka–Volterra core (the ‘‘Explodator’’) and a stabilizing limiting reaction. The new scheme exhibits Hopf bifurcation and limit cycle oscillations. Finally, some possibilities and problems of a generalization are mentioned.
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82.40.Bj Oscillations, chaos, and bifurcations

An alternative to the stoichiometric factor in the Oregonator model

Richard M. Noyes

J. Chem. Phys. 80, 6071 (1984); http://dx.doi.org/10.1063/1.446689 (8 pages) | Cited 12 times

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The original Oregonator model to the Belousov–Zhabotinsky oscillating reaction used three composition variables, five rate constants, and one stoichiometric factor involving five irreversible reaction steps. As a result of objections to the stoichiometric factor by Noszticzius, Farkas, and Schelly, we have developed an alternative model of the same complexity based on six irreversible steps. The revised model eliminates some stoichiometric difficulties, and by minor modification of one of the six steps it handles situations in which the final oxidation state of the reduced bromine is +1, 0, or −1. An alternative skeleton model called the Explodator and proposed by Noszticzius, Farkas, and Schelly should not be considered a viable alternative to the Oregonator unless a computational prerequisite and an experimental kinetic prerequisite can both be satisfied.
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82.40.Bj Oscillations, chaos, and bifurcations
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