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15 Dec 1990

Volume 93, Issue 12, pp. 8415-9209

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Spin–rotation and hyperfine structure in the X 2Σ+ state of yttrium monosulfide by molecular‐beam laser‐radio‐frequency double resonance

Y. Azuma and W. J. Childs

J. Chem. Phys. 93, 8415 (1990); http://dx.doi.org/10.1063/1.459279 (5 pages) | Cited 4 times

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The molecular‐beam laser‐radio‐frequency double‐resonance method has been used to measure the spin–rotation and magnetic hyperfine structure of yttrium monosulfide (YS) in its X 2Σ+ electronic ground state. The spin–rotation constant γ is found to be positive, unlike that of YO. The Fermi contact and dipolar hyperfine interactions (due to the spin I=1/2 of 89Y) are found to be rather close to the corresponding quantities in YO. The contact hfs constant b in the excited B 2Σ+ state of YS was determined by combining the directly measured X 2Σ+ splitting information with B–X optical hfs observations.
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33.15.Pw Fine and hyperfine structure
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.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Spectroscopy and electronic structure of jet‐cooled Al2

Zhenwen Fu, George W. Lemire, Gregory A. Bishea, and Michael D. Morse

J. Chem. Phys. 93, 8420 (1990); http://dx.doi.org/10.1063/1.459280 (22 pages) | Cited 57 times

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Resonant two‐photon ionization spectroscopy has been used to study the jet‐cooled Al2 molecule. The ground state has been conclusively demonstrated to be of 3Πu symmetry, deriving from the σ1gπ1u electronic configuration. High resolution studies have established the bond length of the X3Πu state as re(X3Πu) =2.701±0.002 Å. The third‐law estimate of the Al2 bond strength has been reevaluated using the observed and calculated properties of the low‐lying electronic states to give D00 (Al2)=1.34±0.06 eV. In addition to the previously reported E 2 3Σ−g←X3Πu and F 33Σ−g←X3Πu band systems, the E′ 33Πg←X 3Πu, F″–X, F′–X, G 3Πg←X 3Πu, H′ 3Σ−g←X 3Πu, and H3Δg←X3Πu band systems have been observed for the first time. Bands of the G–X, H′–X, and H–X systems have been rotationally resolved and analyzed, providing rotational constants and electronic state symmetries for the upper states of these systems. A discussion of all of the experimentally known states of Al2 is presented, along with comparisons to previous experimental and theoretical work.
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36.40.-c Atomic and molecular clusters
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Dj Interatomic distances and angles

Optimal phase modulation in stored waveform inverse Fourier transform excitation for Fourier transform mass spectrometry. II. Magnitude spectrum smoothing

Shenheng Guan

J. Chem. Phys. 93, 8442 (1990); http://dx.doi.org/10.1063/1.459281 (4 pages) | Cited 6 times

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A smoothing method for generating optimal SWIFT (stored waveform inverse Fourier transform) excitation waveforms used in Fourier transform mass spectrometry (FT‐ICR or FTMS) was previously proposed to substitute time‐domain waveform apodization procedures. This work gives a detailed analysis of the simple smoothing procedure. The effect of the smoothing procedure on magnitude spectral edges can be easily expressed in analytical format so that the frequency resolution of excitation can be easily analyzed. The relation between the time domain apodization and the smoothing of magnitude spectra in the frequency domain is established. This provides a convenient method to estimate the time duration required for accommodation of excitation power leakage from the power distribution limits. A method for generating nonconstant frequency resolution excitation waveforms is proposed.
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07.75.+h Mass spectrometers

Determination of the electric dipole moment of HN+2

M. Havenith, E. Zwart, W. Leo Meerts, and J. J. ter Meulen

J. Chem. Phys. 93, 8446 (1990); http://dx.doi.org/10.1063/1.459282 (6 pages) | Cited 20 times

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The electric dipole moment of the linear molecular ion HN+2 was determined by measuring the isotope shifts of the rotational g factors of different isotopic species. We studied the Zeeman effect of the R(6) rotational transition at 650 GHz. In a magnetic field of 5.4 T the rotational transition split into two components, separated by 2.2–2.5 MHz. The gR factors were determined for H14N14N+, H14N15N+, and H15N14N+. The dipole moment for H14N14N+ was determined as (3.4±0.2) D, which is in excellent agreement with the theoretical value. The transitions were observed by direct absorption spectroscopy with a tunable FIR sideband spectrometer. The ions were generated in a modified anomalous discharge placed in a superconducting magnet.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.57.+c Magneto-optical and electro-optical spectra and effects
33.20.Ea Infrared spectra

Observation of the 39K2 a 3Σ+u state by perturbation facilitated optical–optical double resonance resolved fluorescence spectroscopy

L. Li, A. M. Lyyra, W. T. Luh, and W. C. Stwalley

J. Chem. Phys. 93, 8452 (1990); http://dx.doi.org/10.1063/1.459283 (12 pages) | Cited 49 times

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Rydberg states of the potassium dimer in the 28 430–29 080 cm−1 and 30 030–30 500 cm−1 regions above the ground state X1Σ+g minimum have been studied using the perturbation facilitated optical–optical double resonance technique (PFOODR). Energy levels in these energy regions have been assigned to both triplet and singlet gerade states based on excitation pattern information as well as intensity considerations. Resolved fluorescence from a mixed triplet–singlet 43Πg ∼1Πg upper state to the ground triplet state a 3Σ+u has been used to construct a potential energy curve for the a 3Σ+u state which is in excellent agreement with recent theoretical results. Since this electronic state and the ground singlet state X1Σ+g share the same dissociation limit, we have determined the dissociation energy for the potassium dimer to be De=4450±2 cm−1.
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36.40.-c Atomic and molecular clusters
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.Fm Bond strengths, dissociation energies

Rotational motion of SF6 inside small pores of silica glass

L. Nikiel and T. W. Zerda

J. Chem. Phys. 93, 8464 (1990); http://dx.doi.org/10.1063/1.459284 (5 pages) | Cited 3 times

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Raman spectra of the ν2 and ν5 vibrational modes of SF6 confined within pores of silica gels of average diameter 12 Å are recorded at pressures varied between 84 and 1827 bars and at temperatures 296, 353, and 398 K. The experimental correlation functions for SF6 inside the pores are compared with the theoretical functions obtained from the extended diffusion model and the Fokker–Planck–Langevin model in order to find relaxation times for the angular momentum. It is shown that although experimental correlation functions of SF6 for neat liquid and inside the pores exhibit similar time and density dependence, the mechanisms of reorientational relaxation are different. At low densities molecules collide mainly with the walls and it is suggested that those collisions are less effective in changing the angular momentum.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
78.30.C- Liquids

Fluorescence study of trivalent americium in fluorozirconate glass

Raúl W. Valenzuela and R. T. Brundage

J. Chem. Phys. 93, 8469 (1990); http://dx.doi.org/10.1063/1.459285 (5 pages) | Cited 6 times

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The fluorescence spectrum of tripositive americium in a fluorozirconate glass at low temperature has been measured. Six fluorescence lines were observed between 515 to 880 nm and identified as Am3+ transitions. Fluorescence decay measurements at 15 K are reported for transitions that originate from states 5D1′ (∼1.0 ms) and 5L6′ (∼17 μs). The 5D1′ state was excited directly to produce fluorescence in order to confirm the assignment of the excited state.
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78.55.Hx Other solid inorganic materials
32.50.+d Fluorescence, phosphorescence (including quenching)

Diode laser probing of the low frequency vibrational modes of baths of CO2 and N2O excited by relaxation of highly excited NO2

James Z. Chou, Scott A. Hewitt, John F. Hershberger, and George W. Flynn

J. Chem. Phys. 93, 8474 (1990); http://dx.doi.org/10.1063/1.459286 (8 pages) | Cited 18 times

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Quenching of highly excited vibrational states of NO2 in baths of CO2 and N2O has been investigated. Dilute NO2 mixtures were excited by a pulse from an excimer pumped dye laser operating at 495 nm. Various vibrational modes of the bath gases were probed with continuous wave IR diode lasers. Less than 20% of the energy initially placed in the NO2 by the dye laser is taken up by the vibrational degrees of freedom of the CO2 or N2O baths. For N2O, the three different vibrational modes (ν1=1285 cm−1, ν2=589 cm−1, ν3=2223 cm−1) take up almost equal amounts of energy from NO2, but the number of vibrational quanta produced in the bath is found to increase with decreasing vibrational frequency. Similar results are found for CO2 except that the ν1 and ν2 modes cannot be studied separately for this bath gas due to rapid ν1↔ν2 intermode equilibration.
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34.50.Ez Rotational and vibrational energy transfer
33.20.Ea Infrared spectra

Fourier transform emission spectroscopy: The B 4Σ−–X 4Σ− transition of BC

W. T. M. L. Fernando, L. C. O’Brien, and P. F. Bernath

J. Chem. Phys. 93, 8482 (1990); http://dx.doi.org/10.1063/1.459287 (6 pages) | Cited 9 times

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The gas‐phase emission spectrum of BC was recorded using a high resolution Fourier transform spectrometer. The BC radical was produced by sputtering in a composite‐wall hollow cathode discharge lamp. The Δv=0 vibrational sequence of the B 4Σ−– X 4Σ− transition near 5590 Å was rotationally analyzed. A set of spectroscopic constants were derived for the 0–0, 1–1, 2–2, and 3–3 vibrational bands, including re =1.491 16(34) Å for the X 4Σ− state and re =1.460 23(29) Å for the B 4Σ− state.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Kf Visible spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

Jet spectroscopy and excited state dynamics of benzyl and substituted benzyl radicals

Masaru Fukushima and Kinichi Obi

J. Chem. Phys. 93, 8488 (1990); http://dx.doi.org/10.1063/1.459710 (10 pages) | Cited 49 times

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Benzyl and its p‐fluoro and p‐methyl derivatives are produced by the ArF laser (193 nm) photolysis of their chlorides in the supersonic free jet. The spectroscopy and excited state dynamics of these radicals are studied by the laser induced fluorescence (LIF) method under the collision free condition. The assignments of vibronic bands are carried out from the LIF excitation and dispersed spectra and the vibrational energies of the D1 state are determined. The excitation spectrum of p‐fluorobenzyl shows quite similar vibrational structure to that of p‐fluorotoluene up to about 1000 cm−1 from the 000 band, which indicates that D2 of p‐fluorobenzyl lies about 1000 cm−1 above D1 and no vibronic coupling exists lower than this energy. On the other hand, benzyl and p‐methylbenzyl show very complicated and irregular vibronic structures in excitation spectra, which are not similar to those of toluene and p‐xylene. This complication is explained by the D1–D2 vibronic coupling caused by low lying D2 states in these radicals. Time profiles of the emission intensity of p‐fluorobenzyl and p‐methylbenzyl show single exponential decay and their lifetimes do not indicate significant dependence on vibronic levels. On the other hand, benzyl shows dual exponential decay, which is interpreted by intermediate coupling case behavior.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Lg Ultraviolet spectra
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Rotational reorientation dynamics of polar dye molecular probes by picosecond laser spectroscopic technique

G. B. Dutt, S. Doraiswamy, N. Periasamy, and B. Venkataraman

J. Chem. Phys. 93, 8498 (1990); http://dx.doi.org/10.1063/1.459288 (16 pages) | Cited 68 times

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Fluorescence lifetimes and rotational reorientation times for four structurally similar dye molecules—three monocations: cresyl violet, nile blue, and oxazine 720 and one neutral but polar: nile red—have been measured by picosecond time‐resolved fluorescence depolarization spectroscopy using the single‐photon counting technique, in a number of solvents, which included a wide range of alcohols, other hydrogen‐bonding liquids, and a few aprotic liquids. The rotational reorientation of the dye probes (assumed to be oblate ellipsoids) are sought to be explained in terms of the Stokes–Einstein–Debye theory and dielectric friction. The individual contributions to the rotational friction due to the above two factors were calculated using reasonable values for the molecular volume and dipole moment of the solute. The rotational behavior of all the four dyes in amides and aprotic solvents is reasonably well explained in terms of the simple stick hydrodynamic model with the ‘‘molecular volume’’ obtained by using the measured rotational reorientation time in water. On the other hand, in order to describe the rotational reorientation dynamics of all the dye molecules in n‐alcohols, it is necessary to include the friction contribution due to the dielectric properties of the solvent. It appears that a change in boundary condition, something intermediate between stick and slip or close to slip, is required to satisfactorily explain the rotational reorientation times of the dye molecules in polyalcohols like ethylene glycol and glycerol. Investigation of the rotational behavior of all the four dyes as a function of viscosity by varying the temperature has been carried out in three solvents: 1‐heptanol, 1‐undecanol, and ethylene glycol. While the rotational reorientation times had a good linear η/T dependence, it was found that at a particular macroscopic viscosity value the rotational reorientation times obtained by the solvent variation and temperature variation are different. From the temperature variation study it was found that there is a satisfactory agreement between the solvent viscosity activation energy and the activation energy obtained for the reorientation rate of the dye probe molecules.
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78.55.Bq Liquids
78.47.-p Spectroscopy of solid state dynamics

A special method for analyzing anisotropic nuclear magnetic resonance parameters: Acetonitrile in liquid crystals

Juhani Lounila, Mika Ala‐Korpela, and Jukka Jokisaari

J. Chem. Phys. 93, 8514 (1990); http://dx.doi.org/10.1063/1.459289 (10 pages) | Cited 9 times

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A reliable analysis of the nuclear magnetic resonance (NMR) spectral parameters of partially oriented molecules requires the calculation of the effects of the correlation between the molecular vibration and rotation. However, in many cases the information content of the spectral data is not sufficient for an unambiguous determination of all the adjustable parameters involved in such an analysis. The present paper describes a special method to simplify the analysis significantly, so as to make seemingly underdetermined problems solvable. The method is applicable to the molecules which contain segments composed of one or more light bonds attached to a heavier bond. It is applied to the anisotropic couplings Dij of acetonitrile (CH3CN) oriented in various liquid crystals. The analysis leads to the following rα geometry: ∠HCH=109.22°±0.06°, rCH/rCC =0.751±0.002 and rCN/rCC =0.788±0.005. In addition, detailed information on (1) the indirect coupling anisotropies ΔJCC and 2ΔJCN, (2) the 1H and 13C chemical shift anisotropies, (3) the external torques acting on the CH bonds, and (4) the orientational order parameters of the CH3C segment of the acetonitrile molecule is obtained.
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33.25.+k Nuclear resonance and relaxation
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
76.60.Es Relaxation effects

The crystalline site symmetry and its effect on the vibrational spectra of a weakly hindered molecule. V. Crystallization effects in NH4B(C6H5)4

Malcolm P. Roberts

J. Chem. Phys. 93, 8524 (1990); http://dx.doi.org/10.1063/1.459290 (11 pages) | Cited 1 time

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Changes in the vibrational spectra for molecules that nearly freely rotate or perform rotational tunneling at low temperatures are explained through the systematic study of the combined symmetry of the molecule, the site, and the molecule’s nuclear spins. The changes observed for different crystallizations in the low temperature vibrational spectra of the NH+4 ion dilute in KTPB and in NH4B(C6D5)4, the NH3D+ ion in ATPB and NH4ClO4, and of solid CH4 II are examined and explained as arising from slight perturbations of the crystalline site symmetry.
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64.70.D- Solid-liquid transitions
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
78.30.Jw Organic compounds, polymers
33.20.Tp Vibrational analysis

Deposition of mass selected silver clusters in rare gas matrices

W. Harbich, S. Fedrigo, F. Meyer, D. M. Lindsay, J. Lignieres, J. C. Rivoal, and D. Kreisle

J. Chem. Phys. 93, 8535 (1990); http://dx.doi.org/10.1063/1.459291 (9 pages) | Cited 58 times

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We report on the successful ‘‘soft landing’’ of size selected silver dimers and trimers in solid krypton matrices. Silver cluster cations, produced by sputtering, were mass selected in a quadrupole mass filter and then codeposited with krypton on a cooled sapphire or CaF2 window in the presence of low energy electrons. Neutralized cluster samples were interrogated in situ by excitation and fluorescence spectroscopy. Deposition of slow (≤20 eV) silver dimer cations gave rise to strong excitation bands (centered at λ=275 and 390 nm) from Ag2 plus the characteristic triplet signal of the atom. The spectra imply that fewer than 25% of the dimers were fragmented during the neutralization and deposition steps. In similar experiments with Ag3 we were able to assign trimer absorption bands at 331, 364, 402, 421, 458, and 514 nm and identify characteristic emission features at 381, 560, and 626 nm.
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36.40.-c Atomic and molecular clusters
33.50.Dq Fluorescence and phosphorescence spectra

Laser spectroscopy of crossed molecular beams: The dissociation energy of BaI from energy‐balance measurements

P. H. Vaccaro, D. Zhao, A. A. Tsekouras, C. A. Leach, W. E. Ernst, and R. N. Zare

J. Chem. Phys. 93, 8544 (1990); http://dx.doi.org/10.1063/1.459292 (13 pages) | Cited 15 times

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Through application of energy‐balance arguments to the crossed‐beam reaction Ba(1S0)+HI(X 1Σ+) →BaI(X 2Σ+) +H(2S1/2), a lower limit for the BaI bond dissociation energy is determined to be D00(BaI) ≳76.8±1.7 kcal/mol (3.33±0.07 eV). Based on the upper bound of D00(BaI) ≲78.5±0.5 kcal/mol, as determined from earlier predissociation studies [M. A. Johnson, J. Allison, and R. N. Zare, J. Chem. Phys. 85, 5723 (1986)], we recommend a BaI bond strength of 77.7±2.0 kcal/mol (3.37±0.09 eV). This dissociation energy is more than 5 kcal/mol higher than the previously accepted value of D00(BaI) as derived from mass spectrometric measurements.
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34.50.Lf Chemical reactions
33.15.Fm Bond strengths, dissociation energies

2+1 resonantly enhanced multiphoton ionization of CO via the E 1Π–X 1Σ+ transition: From measured ion signals to quantitative population distributions

Melissa A. Hines, Hope A. Michelsen, and Richard N. Zare

J. Chem. Phys. 93, 8557 (1990); http://dx.doi.org/10.1063/1.459293 (8 pages) | Cited 32 times

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The 2+1 resonantly enhanced multiphoton ionization (REMPI) spectrum of the CO E 1Π–X 1Σ+ (0,0) transition is used to determine ground state rotational populations with a detection sensitivity of approximately 3×106 molecules per quantum state per cm3. Low rotational states of CO are ionized to CO+; however, high rotational states form both C+ and CO+. This effect is shown to be both branch dependent and J dependent. In order to extract reliable ground state populations, both the C+ and CO+ channels must be measured. When the C+ channel is not accounted for, high rotational states are systematically undercounted. New rotational constants are determined for the C12O16 E 1Π state; Bf0 is 1.9526 cm−1 and Be0 is 1.9645 cm−1. The large lambda doubling (q=0.0119 cm−1 ) of the E state is attributed to a perturbation by the nearby C 1Σ+ state.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants

Vibron–phonon excitations in the molecular crystals N2, O2, and CO by Fourier transform infrared and Raman studies

H. W. Löwen, K. D. Bier, and H. J. Jodl

J. Chem. Phys. 93, 8565 (1990); http://dx.doi.org/10.1063/1.459294 (11 pages) | Cited 18 times

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The influence of temperature on the vibron–phonon combination band in the Raman and infrared (ir) spectra of the N2 and O2 molecular crystals supports the possibility of an assignment of the main features in the sideband to strong contributions from translational and librational phonons in points of high symmetry in the reciprocal lattices. The temperature behavior in Raman and ir sideband spectra in α‐N2 is attributed to distinct anharmonicities in the isotropic and anisotropic parts of the potential and to different coupling mechanisms, resulting in a librational and translational weighted one‐phonon density of states (DOS). In contrast, such an interpretation is not feasible for the poorly structured CO sideband, although the crystal structures of CO and N2 are nearly identical. The difference is attributed to strong anharmonicities and the presence of a weak dipole moment in the former, which introduces strong lattice mode coupling. Crossing the α–β phase transition has marked effects on the sidebands (shape, intensity) in both N2 and O2 crystals, which reflects the orientational disorder in the β phase of the former and the importance of the change in magnetic interactions in the latter. For both molecular crystals, the vibron–phonon coupling to the electromagnetic field is stronger in the ir than in the Raman spectra and seems predominantly due to electrical anharmonicities.
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78.30.Hv Other nonmetallic inorganics
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Rydberg state absorption spectroscopy of Br(CH2)nI (n=1–3)

Abraham Penner and Aviv Amirav

J. Chem. Phys. 93, 8576 (1990); http://dx.doi.org/10.1063/1.459243 (4 pages) | Cited 3 times

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The absorption spectra of jet‐cooled bromoiodomethane (CH2BrI), 1,2‐bromoiodoethane (Br(CH2)2I) and 1,3‐bromoiodopropane (Br(CH2)3I) were measured in the spectral range 1600–2100 Å, and were compared with the corresponding monohalide absorption spectra. A pronounced broadening of the halogen nonbonding→Rydberg transition was observed in CH2BrI and in Br(CH2)2I whereas the transition width was considerably smaller in Br(CH2)3I. These results are rationalized in terms of a mixing of the halogen Rydberg states and the C–X (X=Br,I) antibonding state. The photochemical implications of these spectra are discussed in connection with a possible Rydberg state selective photochemistry.
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33.20.Ni Vacuum ultraviolet spectra
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Molecular beam optical Stark spectroscopy of YF

Jeffrey Shirley, Chris Scurlock, Timothy Steimle, Benoit Simard, Michael Vasseur, and P. A. Hackett

J. Chem. Phys. 93, 8580 (1990); http://dx.doi.org/10.1063/1.459244 (6 pages) | Cited 11 times

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The molecular‐beam‐optical Stark spectrum of the B1Π(v=0)−X 1Σ+(v=0) band system of YF has been recorded and analyzed. The permanent electric dipole moment μ and the magnetic hyperfine parameter a for the B1Π state were experimentally determined to be 2.96(4) D and 146.8(3) MHz and the experimentally determined value for μ(X 1Σ+) is 1.82(8) D. The sign of the magnetic hyperfine parameter indicates that the major contribution to the B1Π state is from a⋅⋅⋅πδ configuration. The determined μ(X 2Σ+) value is compared with theoretical predictions and the ratio μ(X 1Σ+)/μ(B 1Π) is rationalized in terms of plausible molecular orbital descriptions for the two electronic states.
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33.57.+c Magneto-optical and electro-optical spectra and effects
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Pw Fine and hyperfine structure
31.30.Gs Hyperfine interactions and isotope effects

Spectral diffusion and thermal recovery of spectral holes burnt into a phthalocyanine doped Shpol’skiĭ system

J. Zollfrank and J. Friedrich

J. Chem. Phys. 93, 8586 (1990); http://dx.doi.org/10.1063/1.459245 (5 pages) | Cited 7 times

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We measured thermally irreversible line broadening features of photochemical holes burnt into a phthalocyanine doped Shpol’skii crystal. The broadening, as obtained from temperature cycling hole burning experiments is significant, indicating that irreversible structural changes do occur in Shpol’skii matrices. Different sites show a different behavior. As far as line broadening is concerned, the observed features are similar to glasses. The thermal recovery curve of the holes, however, differs very much from glasses. It can be fitted by a bimodal Gaussian distribution. This bimodal distribution is interpreted in terms of two categories of photoproduct states, which the phthalocyanine molecule can possibly occupy: In category one, the two inner protons are neighbors in category two, they are diagonal.
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78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics

Laser‐induced fluorescence of Rb2: The (1)1Σ+g(X), (2)1Σ+g, (1)1Πu(B), (1)1Πg, and (2)1Πu(C) electronic states

C. Amiot

J. Chem. Phys. 93, 8591 (1990); http://dx.doi.org/10.1063/1.459246 (14 pages) | Cited 53 times

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More than 10 000 resolved rotational lines in the (2) 1Πu(C)–(1) 1Σ+g(X), (2) 1Πu(C)–(1) 1Πg, (2) 1Πu(C)–(2) 1Σ+g, (1) 1Πu(B)–(1) 1Σ+g(X), and (1) 1Σ+u(A)–(1) 1Σ+g(X) transitions of Rb2 have been accurately measured with the technique of Fourier‐transform spectroscopy. The wave numbers of all the rotational lines were determined with an accuracy better than 5×10−3 cm−1. A thorough and simultaneous analysis of all the measured data yields molecular constants, potential‐energy curves, and dissociation energies for five different excited electronic states. The observation of highly excited vibrational levels in the fundamental state (v″=112) leads to the value of the energy of dissociation: 3994.4±0.4 cm−1.
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36.40.-c Atomic and molecular clusters
33.50.Dq Fluorescence and phosphorescence spectra
33.20.Sn Rotational analysis
33.15.Fm Bond strengths, dissociation energies

An experimental study of radiation‐induced pure dephasing: ArF excited emission of O2

Y. P. Zhang and L. D. Ziegler

J. Chem. Phys. 93, 8605 (1990); http://dx.doi.org/10.1063/1.459247 (11 pages) | Cited 4 times

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The effects of incoherent incident light on both nonresonant and resonant secondary radiation (RSR) are demonstrated for the spontaneous emission of O2. ArF excimer radiation (FWHH∼120 cm−1) is resonant with several rovibronic features of the v′=4 band of the Schumann–Runge absorption system. Off‐resonant contributions to the RSR spectrum are Raman‐like (v″=1) but carry the linewidth of the incident incoherent radiation. Purely resonant emission features are found to be entirely fluorescence‐like (v″≥6). Other RSR vibrational bands of O2 exhibit contributions of both types of emission including interferences between Raman (off‐resonant) and fluorescence (resonant) amplitudes. The observed depolarization ratios also reflect these various emission characters. The RSR spectra of O2 excited by incoherent (ArF) driving fields are contrasted with that due to monochromatic excitation. Convolution of the incident spectral density with a rovibronic Kramers–Heisenberg irreducible tensor treatment of resonance Raman scattering cross sections is shown to capture all the observed RSR emission characteristics.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Fb Raman and Rayleigh spectra (including optical scattering)

Electron impact excitation of coronene

M. A. Khakoo, J. M. Ratliff, and S. Trajmar

J. Chem. Phys. 93, 8616 (1990); http://dx.doi.org/10.1063/1.459248 (4 pages) | Cited 14 times

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A preliminary study of the electron‐impact excitation of thermally evaporated coronene at 550° C was carried out using electron‐energy‐loss spectroscopy. Measurements of the energy‐loss spectra of coronene at high (100 eV) and low (5–20 eV) impact energies are presented. One of the high‐energy spectra was converted to an apparent generalized oscillator strength spectrum and compared to the photoabsorption spectrum of coronene. Observations concerning vibrational excitation of coronene by electron impact are also presented and discussed.
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34.80.Gs Molecular excitation and ionization

Rotationally resolved vibrational overtone spectroscopy of hydrogen peroxide at chemically significant energies

X. Luo and T. R. Rizzo

J. Chem. Phys. 93, 8620 (1990); http://dx.doi.org/10.1063/1.459249 (14 pages) | Cited 42 times

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An infrared–optical double resonance scheme simplifies the room temperature 6νOH vibrational overtone spectrum of hydrogen peroxide and prepares highly excited reactant molecules in single rotational states for unimolecular reaction studies. First, an optical parametric oscillator excites the OH asymmetric stretch (ν5) and selects a single or small subset of rotational states. A visible dye laser pulse then promotes molecules from vOH=1 to vOH=6 where they subsequently dissociate to produce two OH fragments. A third laser detects the dissociation products via laser induced fluorescence. The rotationally resolved vibrational overtone spectra of hydrogen peroxide generated by scanning the visible dye laser frequency are assignable to a parallel band of a near prolate symmetric top. Linewidths of the individual rovibrational features range from 1–3 cm−1 but show no systematic dependence upon the rotational quantum numbers and are attributed predominantly to anharmonic coupling of the zeroth‐order bright state to dark background states. The assignability of the double‐resonance vibrational overtone spectra to J and K quantum numbers implies that K is conserved for at least a time determined by the linewidth of a single zeroth‐order rovibrational feature.
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33.20.Ea Infrared spectra
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.Sn Rotational analysis
33.70.Jg Line and band widths, shapes, and shifts

Rotationally specific mode–to–mode vibrational energy transfer in D2CO/D2CO collisions. I. Spectroscopic aspects

C. P. Bewick and B. J. Orr

J. Chem. Phys. 93, 8634 (1990); http://dx.doi.org/10.1063/1.459250 (9 pages) | Cited 11 times

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Time‐resolved infrared‐ultraviolet double‐resonance (IRUVDR) spectroscopy is used to look for rotationally specific channels in collision‐induced vibrational energy transfer between the ν6 and ν4 modes of D2CO. The efficiency of such V‐V transfer has been shown in previous work to be enhanced by a combination of Coriolis coupling and rotor asymmetry. IRUVDR spectra, recorded in pure D2CO vapor with a range of delay intervals between IR pump and UV probe laser pulses, reveal (J,Ka) ‐dependent propensities in the resulting ν6→ν4 transfer arising from D2CO/D2CO collisions. At the same time, rotational relaxation within the rovibrational manifold (v6=1) initially prepared by the IR pump laser is found to be more pronounced than the growth of population in the neighboring v4=1 manifold, due to ν6→ν4 transfer. This trend is shown to be reversed in the case of D2CO/N2O collisions, where the effects of rotational relaxation appear to be less pronounced than those of ν6→ν4 transfer. This work, performed with spectroscopic resolution superior to that in previous investigations, has demonstrated a number of new effects, including the identification of weakly allowed t‐type (ΔKa=3) features in the IRUVDR spectra. It also provides the spectroscopic background to paper II of this series, which explores the detailed kinetics of (J,Ka) ‐resolved ν6→ν4 transfer in D2CO.
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34.50.Ez Rotational and vibrational energy transfer
33.20.Ea Infrared spectra
33.20.Lg Ultraviolet spectra
34.50.-s Scattering of atoms and molecules
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