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1 Apr 1986

Volume 84, Issue 7, pp. 3589-4114

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Semiclassical vibration–rotation spectra of gaseous and physisorbed molecules

John E. Adams

J. Chem. Phys. 84, 3589 (1986); http://dx.doi.org/10.1063/1.450194 (9 pages) | Cited 18 times

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A semiclassical spectral intensity method is applied to the calculation of vibration–rotation spectra both of isolated molecules and of molecules physically adsorbed on a solid surface. For the case of an isolated HCl molecule, we are able to generate discrete vibration–rotation spectral lines, the frequencies and integrated intensities of which agree well with the available literature values. Line shapes obtained for this case exhibit no evidence of broadening beyond the theoretical resolution of the calculation. Physisorption of the HCl on an Ar(111) surface leads, however, to a collapse of the R, P band structure at low rotational energies, with the free rotor dynamical limit being reached only at higher energies. The transition between dynamical regimes is associated with substantial line broadening and shifts in the line centers as well as with an increase in the desorption rate. A loss of rotational phase coherence appears to represent the principle line broadening mechanism in the present calculations.
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33.20.Ea Infrared spectra
33.20.Vq Vibration-rotation analysis
33.70.Fd Absolute and relative line and band intensities

Spontaneous vibrational decay rate in the KF electronic ground state

David R. Bedding and Thomas I. Moran

J. Chem. Phys. 84, 3598 (1986); http://dx.doi.org/10.1063/1.450195 (5 pages)

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We have measured the spontaneous vibrational decay rates in the KF electronic ground state for v=2 → 1 and v=1 → 0 transitions in both the J=1 and the J=2 rotational states using a velocity selected molecular‐beam technique. The four decay rates are self‐consistent and reduce to a 1 → 0 decay rate of 2.6±0.4 s−1, which agrees with rates inferred from spectroscopic data.
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33.20.Tp Vibrational analysis
07.77.-n Atomic, molecular, and charged-particle sources and detectors
37.20.+j Atomic and molecular beam sources and techniques

Photoelectron study of the valence level cross sections of XeF2 from 21 to 50 eV photon energy

B. W. Yates, K. H. Tan, G. M. Bancroft, L. L. Coatsworth, J. S. Tse, and G. J. Schrobilgen

J. Chem. Phys. 84, 3603 (1986); http://dx.doi.org/10.1063/1.450196 (7 pages) | Cited 15 times

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Using monochromatized synchrotron radiation, the gas phase photoelectron spectra of the first five valence orbitals of XeF2 have been obtained from 21–50 eV photon energy. From these spectra, the branching ratios and partial cross sections have been calculated. Theoretical branching ratios and partial cross sections have been obtained from MS‐Xα calculations and compared with experiment. The generally good agreement between experiment and theory confirms the DV‐Xα and MS‐Xα orbital assignments: 5πu <10σg <3πg <4πu <6σu, in order of increasing binding energy. Somewhat surprisingly because of the lack of antibonding virtual orbitals above threshold and the long Xe–F bond length (2.00 Å), a number of strong resonances are predicted and observed. For example, resonances are predicted at 4.8 (πg channel), 11.6 (πu, δu channels), and 14.3 eV (σu channel) kinetic energies. The observed resonance positions are usually in reasonable agreement with these. The nature of these resonances are discussed, and compared to similar features in O2, F2, and CO2.
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33.60.+q Photoelectron spectra

The effect of pressure on the Raman spectra of solids. III. Sodium formate, NaHCOO

A. M. Heyns

J. Chem. Phys. 84, 3610 (1986); http://dx.doi.org/10.1063/1.450197 (7 pages) | Cited 10 times

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The pressure dependence of the Raman bands of NaHCOO has been studied at 298 K and three different phases were identified up to pressures of 30 kbar. Phase II is the one stable at ambient conditions, and when heated to 500 K at ambient pressures it undergoes a transition to phase I. This transition has also been studied and the frequencies of the Raman‐active librations of NaHCOO I resemble those of aqueous solutions of formate ions. From the shifts in the librations which accompany the I–II transition it can be concluded that the Na+–HCOO− interactions are much weaker in phase I than phase II. The Raman spectrum of KHCOO II at ambient conditions is also reported and resemblances between this spectrum and that of NaHCOO III are discussed.
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78.30.Jw Organic compounds, polymers
64.70.K- Solid-solid transitions
62.50.-p High-pressure effects in solids and liquids
78.30.Hv Other nonmetallic inorganics

The effects of excited‐state diffusion and saturation on the strong field reflection and transmission properties of materials

Yehuda B. Band and G. Sewell

J. Chem. Phys. 84, 3617 (1986); http://dx.doi.org/10.1063/1.450198 (7 pages)

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We propose a method for calculating the effects of saturation of optical transitions (and other nonlinear polarization mechanisms), and the effects of particle diffusion, on the reflection and transmission of light through a medium when surface reflections are important. We use a multiple shooting technique to solve the two‐point boundary value problem specified by the nonlinear wave equation for the electric field and the rate equation for the excited state population density of the medium, and their boundary conditions. The method can be used to describe both saturable absorption of organic dyes in a Fabry–Perot cavity and strong field reflection and transmission of semiconductors. As an illustrative example, the intensity dependence of the reflection and transmission from a slab of InSb is calculated.
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78.20.-e Optical properties of bulk materials and thin films

Fluorescence lifetimes and Zeeman quantum beats of single rotational levels in 3B2 carbon disulfide

Gary W. Loge, J. J. Tiee, and F. B. Wampler

J. Chem. Phys. 84, 3624 (1986); http://dx.doi.org/10.1063/1.450199 (6 pages) | Cited 13 times

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The lowest observed triplet state of carbon disulfide, the R 3B2 state, was directly excited using a pulsed, narrow bandwidth dye laser (0.05 cm−1). The first reported collision‐free lifetimes of this state of CS2 were obtained, and the changes in lifetime for single rotational and vibrational levels were observed. The effect of rotation and vibration on the lifetimes indicates that the R 3B2 state has strong spin‐orbital coupling with the higher lying V 1B2 state, which gives the R 3B2 state such short lifetimes (2–5 μs) for a triplet state. A magnetic field was observed to have no effect on the lifetimes, which is consistent with this strong spin‐orbital coupling scheme. Zeeman quantum beats were observed on the fluoresence decay curves in a magnetic field. Beat frequencies were obtained as a function of magnetic field strength to obtain permanent magnetic dipole moments for the R 3B2 state vibrational levels. The magnetic dipole moments were found to be independent of rotational angular momentum (N dependence) indicating a strong spin‐orbital coupling, consistent with the lifetime data. The collisional depolarization rate was qualitatively observed to be competitive with and slightly faster than electronic quenching.
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33.50.Dq Fluorescence and phosphorescence spectra
33.57.+c Magneto-optical and electro-optical spectra and effects
33.70.Fd Absolute and relative line and band intensities

Rotational resolution of the NeCl2 B ← X 9–1 transition

Dwight D. Evard, Fritz Thommen, and Kenneth C. Janda

J. Chem. Phys. 84, 3630 (1986); http://dx.doi.org/10.1063/1.450200 (4 pages) | Cited 31 times

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High resolution (∼0.001 cm−1) laser induced fluorescence spectra of the (9–1) rovibronic band of the B3Π0+ ← X 1Σg+ system of Cl2 and the associated van der Waals molecule NeCl2 have been obtained in a free jet expansion of Ne, Cl2, and He. The spectrum of NeCl2 associated with the (9–1) transition of the free Cl2 molecule was observed 5.46 cm−1 to the blue of the band origin of uncomplexed Cl2. This study confirms the previously reported observation of a metastable vibrationally excited ground electronic state of NeCl2. Although the energy in the Cl2 stretching vibration is an order of magnitude larger than the Ne–Cl2 dissociation energy, no dissociation is observed on the microsecond time scale. This study also significantly refines the structural parameters obtained from the previous low resolution work. Rotational resolution was achieved and a detailed rotational assignment was made which allowed the Ne to Cl2 center of mass distance to be determined. This distance is 3.565±0.035 Å in the ground state, and 3.536±0.036 Å in the excited state. The structure of the NeCl2 van der Waals molecule is T‐shaped, with the dipole transition moment lying along the Cl2 bond axis, giving a ‘‘b‐type’’ asymmetric top spectrum. The vibrational predissociation lifetime in the B(v′=9) state was found to be 258±42 ps on the basis of homogeneous broadening.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.15.Dj Interatomic distances and angles

The magnetic circular dichroism of 1‐azabicyclo[2,2,2]octane (ABCO) in the n0→3p region

Aharon Gedanken

J. Chem. Phys. 84, 3634 (1986); http://dx.doi.org/10.1063/1.450201 (4 pages) | Cited 1 time

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An MCD and absorption spectra measured in the energy region of the second excited state of 1‐azabicyclo[2,2,2]octane (ABCO) reveal large positive A terms. Simple calculations of the magnetic moment of a 1E excited state yield also a positive sign for the A terms. A small negative B term is observed 355 cm−1 below the origin of the 1E state. Based on B term calculations we assign it as the 1A1→1A1 transition (n0→3pz). The results are compared with a recent MPI study in the same energy range.
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33.20.Lg Ultraviolet spectra
33.55.+b Optical activity and dichroism
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Shape resonances in the photoionization of CF4

J. A. Stephens, Dan Dill, and J. L. Dehmer

J. Chem. Phys. 84, 3638 (1986); http://dx.doi.org/10.1063/1.450202 (9 pages) | Cited 24 times

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Calculations of photoionization cross sections and photoelectron angular distributions have been performed for all occupied orbitals of CF4 using the multiple‐scattering model. Results are compared with very recent experiments which employ synchrotron radiation to measure these quantities, namely the measurements of Truesdale et al. for the carbon K shell, and measurements of Carlson et al. and Novak et al. for the five outermost valence levels. The calculations predict intense shape resonances below 3 eV in continua of a1 and t2 final state symmetry. Qualitative agreement is attained on comparing much of the theory with experiment, notably the five outer valence levels, which serves to establish a one‐electron picture of the photoionization dynamics of CF4.
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33.60.+q Photoelectron spectra
33.80.Eh Autoionization, photoionization, and photodetachment

Alignment of excited states following multiphoton excitation

W. J. Kessler and E. D. Poliakoff

J. Chem. Phys. 84, 3647 (1986); http://dx.doi.org/10.1063/1.450203 (6 pages) | Cited 9 times

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We report the measurement of the fluorescence anisotropy from excited neutral NO∗(A 2∑+) molecules produced by two‐photon excitation, thus providing a measure of their alignment. The degree of fluorescence anisotropy depended on the excitation pathway, and the results for the fluorescence angular distributions following excitation via the O12 rotational branch were more anisotropic than the superimposed R12,Q22 branch results. Results are given for other rotational branches as well and they should serve as useful aids in photoelectron asymmetry studies following multiphoton ionization, where the alignment of the neutral target state directly influences the photoelectron asymmetries in the ionization step.
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33.80.Wz Other multiphoton processes
33.50.Dq Fluorescence and phosphorescence spectra

Analysis of the absorption spectra of complex pentavalent actinide halides: LiUF6, α‐NaUF6, and CsUF6

H. G. Hecht, J. G. Malm, J. Foropoulos, and W. T. Carnall

J. Chem. Phys. 84, 3653 (1986); http://dx.doi.org/10.1063/1.450204 (10 pages) | Cited 4 times

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Absorption spectra of polycrystalline samples of LiUF6, α‐NaUF6, and CsUF6 have been recorded at 4, 77, and 298 K. This group of compounds has a common sixfold U–F coordination that approaches an octahedral site symmetry for LiUF6 but exhibits increasing trigonal distortion (D3d symmetry) along the indicated series. Spectra have been systematically interpreted as consisting of sequences of vibronic transitions coupled to well‐defined electronic excited states. Crystal‐field calculations have been performed.
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78.40.Ha Other nonmetallic inorganics
71.70.Ch Crystal and ligand fields

Microwave spectrum, conformation, and low frequency vibrational spectrum of cyclopropylisothiocyanate

J. R. Durig, A. B. Nease, R. J. Berry, J. F. Sullivan, Y. S. Li, and C. J. Wurrey

J. Chem. Phys. 84, 3663 (1986); http://dx.doi.org/10.1063/1.450205 (9 pages) | Cited 1 time

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The microwave spectrum of cyclopropylisothiocyanate, c‐C3H5NCS, has been investigated in the region from 12.5 to 40.0 GHz. Two sets of a‐type R‐branch transitions were observed and assigned, on the basis of the rigid rotor model, to the trans and cis conformers. One excited vibrational state for each conformer was also identified and tentatively assigned as the asymmetric NCS torsion. The B and C rotational constants in the ground vibrational state for the trans and cis conformers of c‐C3H5NCS were found to be: B=1122.689±0.002, C=1095.619±0.002 MHz, and B=1346.859±0.003, C=1309.166±0.002 MHz, respectively. The values of the A rotational constants for both conformers were not well determined because the measured transitions are not very sensitive to these constants. The dipole moment components were determined for the trans conformer from the Stark effect to be ‖μa‖=3.11±0.02, ‖μc‖=0.62±0.01, and ‖μt‖=3.17±0.01 D and for the cis conformer to be ‖μa‖=3.34±0.01, ‖μb‖=0.27±0.07, and ‖μt‖=3.35±0.01 D. With reasonably assumed structural parameters for the cyclopropyl moiety and bond distances for the isothiocyanate group, the other structural parameters were calculated from the rotational constants by the diagnostic least squares method to be: r(C–N)=1.390±0.016 Å,∢CNC=143.8±4.2 °, and ∢CCN=118.7±0.1 ° for the trans conformer and r(C–N)=1.414±0.017 Å, ∢CNC=144.4±1.1, and ∢CCN=118.6±2.3 ° for the cis conformer. The far infrared spectrum of the vapor was also recorded and the C–N=C bend was observed at ∼104 cm−1 but little evidence could be found for the second conformer in the vibrational spectrum. These results are compared to the corresponding ones in some related molecules.
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33.20.Bx Radio-frequency and microwave spectra
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Dj Interatomic distances and angles

Lifetime measurements of selectively excited rovibronic levels of SO2

R. Kullmer and W. Demtröder

J. Chem. Phys. 84, 3672 (1986); http://dx.doi.org/10.1063/1.450206 (7 pages) | Cited 18 times

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With a frequency doubled single mode cw dye laser, pulse modulated with a Pockels cell, lifetimes of selectively excited rovibronic levels of SO2 molecules in a collimated molecular beam have been measured. Under collision‐free conditions single exponential decay curves were found for all observed levels. Their radiative lifetimes scatter considerably for the different levels. For the Clements band ‘‘E’’ a mean unperturbed lifetime of about 8 μs was found while for the band at λ=322.6 nm the average lifetime was 30 μs. Possible perturbations are discussed and experimental evidence is given which explains the causes of the greatly differing lifetimes.
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33.20.Lg Ultraviolet spectra
33.70.Fd Absolute and relative line and band intensities
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Properties of the short‐lived triplet states of pyridazine and 3,6‐dichloropyridazine studied by a time‐resolved EPR method

Masahide Terazima, Seigo Yamauchi, and Noboru Hirota

J. Chem. Phys. 84, 3679 (1986); http://dx.doi.org/10.1063/1.450207 (9 pages) | Cited 16 times

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The magnetic and decay properties of the short‐lived triplet (T1) states of pyridazine and 3,6‐dichloropyridazine (DCP) were studied by means of time‐resolved EPR with laser excitation. The zfs of DCP in the p‐dibromobenzene (DBB) host are X=0.094 cm−1, Y=−0.164 cm−1, and Z=0.070 cm−1, and the nitrogen hfcc are Ax=27 G, Ay=18 G, and Az=25 G, which confirms the nπ∗ character of the T1 state. Similar zfs were obtained for DCP and pyridazine in other environments. The sublevel decay rate constants and the relative populating rates were determined from the analysis of the transient EPR signals measured at 3.0 K where the effect of the spin lattice relaxation can be neglected. It was found in both systems that ky is much greater than kx, kz as predicted by a simple group theoretical consideration. ky of DCP and pyridazine were determined to be on the order of 106 s−1, being larger than that of pyrimidine by a factor of ∼104. The reasons for the large ky are discussed, particularly, in terms of the distorted potential of the T1 state.
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33.35.+r Electron resonance and relaxation

Analysis of saturation transfer electron paramagnetic resonance spectra in terms of amplitude and phase

Y. Shimoyama and H. Watari

J. Chem. Phys. 84, 3688 (1986); http://dx.doi.org/10.1063/1.450208 (6 pages) | Cited 5 times

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A systematic analysis of saturation transfer (ST) electron paramagnetic resonance spectroscopy was developed to separate an observed absorption signal either into an amplitude and a phase spectrum or into an in‐phase and an ST spectrum. We established a phase reference procedure, replacing the low‐power phase null method by a high‐power phase maximum method. This is an extension of the finding that a peak‐to‐peak height and a single integration of the second harmonic absorption display vary sinusoidally as functions of the modulation phase [Y. Shimoyama and H. Watari, Appl. Spectrosc. 39, 170 (1985)]. Based on the sinusoidal variation in the peak‐to‐peak height, we found a phase shift at each magnetic field and could evaluate the amplitude and phase of a signal vector. The sinusoidal variation of the single integrated value allowed the absorption signal to be separated into an in‐phase and an ST spectrum. The high‐power phase maximum method provides a remedy of the phase setting problem in ST spectroscopy by which the in‐phase signal can be detected at any microwave field.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
33.35.+r Electron resonance and relaxation

Electron capture phosphoranyl radicals in x‐irradiated diphosphine disulfides. A single crystal ESR and ab initio quantum chemical study

René A. J. Janssen, Max H. W. Sonnemans, and Henk M. Buck

J. Chem. Phys. 84, 3694 (1986); http://dx.doi.org/10.1063/1.450209 (15 pages) | Cited 7 times

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An electron spin resonance (ESR) study of phosphorus centered electron capture radicals trapped in single crystals of substituted diphosphine disulfides [R2P(S)P(S)R2, R=Me, Et, Ph] irradiated with x rays at 77 K is reported. The principal values and direction cosines of the hyperfine and g tensors were determined. It is shown that in all three compounds a three‐electron P–P bond radical is formed. The unpaired electron is found to be symmetrically distributed over the two phosphorus atoms. The direction of the phosphorus hyperfine coupling makes an angle of 20°–30° with the P–P bond. The alkyl substituted diphosphine disulfides reveal furthermore a radical in which the unpaired electron is asymmetrically distributed over the two phosphorus atoms. The electronic configuration of these radicals is best described as trigonal bipyramidal (TBP) with a central phosphorus atom and the unpaired electron in an equatorial position (TBP‐e). The second phosphorus atom and a sulfur substituent are located on the apical sites of the TBP. Irradiation yields for R=Et, Ph also a three‐electron P–S bond radical and a number of dissociation products. Ab initio quantum chemical calculations of the isotropic and anisotropic hyperfine couplings for the three‐electron P–P bond radicals are in good agreement with the experimental values and support the assignment.
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82.50.-m Photochemistry
76.30.Rn Free radicals
71.70.Jp Nuclear states and interactions

Laser induced fluorescence of HCCO (DCCO) radical formed in O+C2H2 (C2D2) reaction

Gen Inoue and Makoto Suzuki

J. Chem. Phys. 84, 3709 (1986); http://dx.doi.org/10.1063/1.450210 (8 pages) | Cited 14 times

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Laser induced fluorescence of HCCO (DCCO) radical have been obtained in the reaction of O(3P)+C2H2(C2D2) for the first time (X 2A′–2A″). The laser excitation spectra have been obtained over the wavelength region from 310 to 370 nm. The collision‐free lifetimes for HCCO and DCCO are 0.14 and 3.8 μs, respectively. From the excitation and dispersed fluorescence spectra, some vibrational energies have been obtained in cm−1 unit: 1762 (1727), 150–140 (n.a.), and 2334 (1901) for the ground state HCCO (DCCO), and 1183 (1167), 866 (607), and 2862 (2075) for the excited state HCCO (DCCO). The band origin ν00 is 28 296.7 cm−1.
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82.33.Vx Reactions in flames, combustion, and explosions
82.20.Hf Product distribution
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
33.20.Tp Vibrational analysis

Methods for analyzing spectroscopic line shapes. NMR solid powder patterns

D. W. Alderman, Mark S. Solum, and David M. Grant

J. Chem. Phys. 84, 3717 (1986); http://dx.doi.org/10.1063/1.450211 (9 pages) | Cited 84 times

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A new method is described for numerically computing theoretical NMR powder patterns which achieves a many‐fold increase in speed and accuracy over previous techniques. The method incorporates a simple and efficient technique for selecting the set of crystal orientations over which the spectral frequencies are calculated. The orientation selection technique is then integrated with an interpolation scheme which transfers the intensities at these frequencies to the computed spectrum. The method will be useful whenever an average over a sphere is computed numerically. The new efficiency of the method makes practical least squares fitting of theoretical spectra to experimental NMR data. The fits provide unbiased estimates of the NMR parameters and their errors. The technique is illustrated by extracting chemical shift tensors from a proton decoupled carbon‐13 NMR spectrum.
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76.60.Es Relaxation effects

Raman study of low frequency lattice modes in dipalmitoylphosphatidylcholine (DPPC) multilayers

E. Jürgens, J. Geurts, W. Richter, and E. Sackmann

J. Chem. Phys. 84, 3726 (1986); http://dx.doi.org/10.1063/1.450212 (5 pages) | Cited 4 times

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Low frequency Raman spectra (6–30 cm−1) of macroscopically ordered multilayers of dipalmitoylphosphatidylcholine (DPPC) were taken as a function of temperature (80–270 K) and for different water contents. A weak band is observed which is shifted from 18.5 to 14 cm−1 between 80 and 270 K. This band is shifted to lower frequencies with increasing water content. In addition, a strong background appears at the Rayleigh line position which grows strongly with increasing temperature. The low frequency band can be explained (1) in terms of an optical mode associated with an antiphase in‐plane vibration of two opposing monolayers or it can (2) be attributed to rotational vibrations of the hydrocarbon chains. The softening of this band is attributed to a decrease in the chain orientational order with increasing temperature. The increasing rotational freedom is expected to cause a transition from a monoclinic or orthorhombic to a hexagonal lattice and eventually triggers the Lβ′ → Lα chain melting transition (at T=340 K for 5.3 wt. % of water). The appearance of the background can also be attributed to an increasing anharmonicity of the lattice potential upon approaching the phase transition, which leads to mode coupling. The possibility of ferroelectric order due to a collective orientation of the dipole moments of the C–O groups of the glycerol backbone is discussed.
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87.16.D- Membranes, bilayers, and vesicles
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.30.Jw Organic compounds, polymers

A singular perturbation approach to non‐Markovian escape rate problems with state dependent friction

M. M. Dygas, B. J. Matkowsky, and Z. Schuss

J. Chem. Phys. 84, 3731 (1986); http://dx.doi.org/10.1063/1.450213 (8 pages) | Cited 8 times

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We employ singular perturbation methods to examine the generalized Langevin equation (GLE) with state and memory dependent friction. The GLE describes the dynamics of a Brownian particle in an arbitrary potential field, acted on by a fluctuating force characterizing the collisions between the particle and the thermal bath. We consider the situation in which the collisions are not restricted to occur instantaneously and additionally these interactions are nonlinear. This leads to a non‐Markovian description of the dynamics of the particle. We compute explicit analytical expressions for the mean exit time τ of the Brownian particle from the potential well in which it is confined. Thus we derive expressions for the activation rate κ from the well, which is inversely proportional to τ. In the examples considered, the effect of the state dependent friction is to increase τ and thus to lower κ.
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05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Vibrational distributions of CN(X 2Σ+) resulting from the C(3P)+NO and C(3P)+N2O reactions at 300 K

Hiroshi Sekiya, Masaharu Tsuji, and Yukio Nishimura

J. Chem. Phys. 84, 3739 (1986); http://dx.doi.org/10.1063/1.450214 (6 pages) | Cited 15 times

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The C(3P) atoms have been prepared from the dissociation of CO molecules by Ar(3P2,0) or He(2 3S) atoms in a flowing afterglow apparatus. The CN(B 2Σ+ ← X 2Σ+) laser induced fluorescence spectra have been observed from the reactions C(3P)+NO → CN(X 2Σ+)+O and C(3P)+N2O → CN(X 2Σ+)+NO at 300 K. The CN(X) state is observed in the vibrational levels up to v″=5 for the C(3P)+NO reaction, while it is detected up to v″=6 for the C(3P)+N2O reaction. In the C(3P)+NO reaction, the relative vibrational populations of CN(X) decrease with increasing the vibrational quantum number and the observed distribution is close to the ‘‘prior’’ one. In contrast to the C(3P)+NO reaction, the vibrational distribution of CN(X,v″=0–6) from the C(3P)+N2O reaction is inverted with a peak at v″=4. This agrees with the previous observation of Dorthe et al. However, the CN(A 2Π → X 2Σ+) chemiluminescence observed by them has never been detected.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.33.Vx Reactions in flames, combustion, and explosions
82.20.Rp State to state energy transfer

The classical mechanics of vibrational predissociation: A model based study of phase space structure and its influence on fragmentation rates

Stephen K. Gray, Stuart A. Rice, and D. W. Noid

J. Chem. Phys. 84, 3745 (1986); http://dx.doi.org/10.1063/1.450215 (8 pages) | Cited 47 times

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The classical dynamics pertinent to van der Waals molecule vibrational predissociation of a T‐shaped model for HeI2(B) is examined. An interesting phase space structure involving nonlinear resonances and stochastic motion is found. For low initial vibrational excitations of the I2 partner of the vdW complex the relevant part of phase space is dominated by quasiperiodic motion indicating a purely quantal mode of decay (‘‘dynamical tunneling’’), but for higher initial vibrational excitations van der Waals molecule predissociation is a classically allowed process. Classically determined rates of decay agree to within a factor of 3 with the rates calculated from quantum mechanics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.20.Tp Vibrational analysis

Measurement of chemiluminescence polarization as a function of collision velocity by time‐of‐flight spectroscopy: Reactions of Xe∗ with HCl, HBr, Cl2, Br2, and I2

Mattanjah S. de Vries, George W. Tyndall, Cathy L. Cobb, and Richard M. Martin

J. Chem. Phys. 84, 3753 (1986); http://dx.doi.org/10.1063/1.450216 (9 pages) | Cited 17 times

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A new method is described for obtaining chemiluminescence polarization as a function of reactant relative velocity, employing a beam‐gas time‐of‐flight technique. These experiments provide information about product alignment as a function of velocity. Results are reported for the formation of xenon halide excimers from the reactions of Xe(3P2,0) with HCl, HBr, Cl2, Br2, and I2. The HX reactions give strong excimer polarization, primarily due to kinematic constraints, whereas with the X2 reactions the excimers are polarized due to the collision dynamics. In this work we have made the first observation of cases in which the products rotate preferentially in planes normal to the initial relative velocity vector. This is observed for the Xe∗+Cl2 and Br2 reactions at low velocities, and is attributed to a mechanism which gives preferential repulsive energy release perpendicular to the reactant relative velocity vector. The direct interaction product repulsion (DIPR) model does not give agreement with the data, showing that a more realistic potential surface model will be necessary to explain the present results.
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78.60.Ps Chemiluminescence
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Orientation, alignment, and hyperfine effects on dissociation of diatomic molecules to open shell atoms

Yehuda B. Band, Karl F. Freed, and Sherwin J. Singer

J. Chem. Phys. 84, 3762 (1986); http://dx.doi.org/10.1063/1.450217 (9 pages) | Cited 23 times

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We demonstrate how magic angle detection of the circular polarization ratio can be used to probe the orientation of open shell atomic photofragments produced in photodissociation with circularly polarized light. The orientation provides new information concerning the dynamics of photodissociation which supplements that available from the alignment or from angular distribution measurements. The general theory of alignment and orientation is provided for photodissociation of diatomic molecules to open shell atoms and incorporates the asymptotic nonadiabatic interactions. Hyperfine depolarization factors are computed and tabulated for the first excited 2P3/2,1/2 states of a number of alkali atoms. They are used to transform between theoretical electronic orientation and alignment and experimentally observed values in the limit where the nuclear spins are unpolarized prior to photodissociation and where hyperfine transitions are not separated in the detection process. Orientation and alignment parameters are calculated for a variety of photodissociations in the high energy axial recoil limit.
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33.80.Gj Diffuse spectra; predissociation, photodissociation

Dissociative single and double photoionization of N2: Analytical photoion spectroscopy

Toshio Masuoka and Hiroshi Fujikawa

J. Chem. Phys. 84, 3771 (1986); http://dx.doi.org/10.1063/1.450218 (5 pages) | Cited 7 times

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Observed branching ratios for the fragment ions N+ produced in dissociative photoionization of N2 have been differentiated with respect to photon energy. The results indicate dissociation channels of the parent ions and the molecular Rydberg states into the fragment ions. The mechanisms of dissociative photoionization have been discussed by comparing the observed differential spectra with the known ionic states including those such as the multielectron bands observed in photoelectron spectra and the double ionization states observed in Auger spectra. It becomes evident that these ionic states play an important role in producing the fragment ions.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.60.+q Photoelectron spectra
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