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  • 1
    Electronic Resource
    Electronic Resource
    Photoionization of rotationally cooled H2O and D2O in the region 650–990 A(ring) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3302-3314 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Room temperature and rotationally cooled relative photoionization cross sections for H2O and D2O were determined in the wavelength region 650–990 A(ring) with a wavelength resolution of 0.06–0.11 A(ring) (∼7–12 cm−1 ); the spectra were normalized to the absolute photoionization cross sections determined by Katayama et al. [D. H. Katayama, R. E. Huffman, and C. L. O'Bryan, J. Chem. Phys. 59, 4309 (1973)] with lower resolution. A rotational analysis of the Π subbands in the (0,6,0) and (0,8,0) bands of the (A˜ 2A1)3db11B1←X˜1A1 Rydberg transition determined the symmetry of the upper state; in addition, the series was extended to higher principal quantum numbers. The analysis of these and other bands was made difficult both by the large natural linewidths of the rotational transitions and by the absence of transitions to rotational levels with N'(approximately-greater-than)3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459805
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  • 2
    Electronic Resource
    Electronic Resource
    A beam experiment on excimer formation in collisions of Kr*(3P0), Kr*(3P2), and Xe* atoms with Br-containing molecules (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7903-7925 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reactions of metastable Kr* and Xe* atoms with several Br-containing molecules are studied with a beam-gas experimental apparatus. For Kr*, state selection of the metastable atom beam is employed to investigate the influence of the initial fine-structure state Kr*(3P0) and Kr*(3P2) on the reaction. Trial-and-error simulation of the observed emission spectra results in modified potential energy curves for the X, A(3/2), B, and C states of the KrBr and XeBr excimer products and corresponding transition moments. The propensity for conservation of the Kr+(2P1/2) ion core in the reactions of Kr*(3P0) is observed to be between 36% and 51%, depending on the target, while for the Kr+(2P3/2) core the propensity is close to 100%. This is in general agreement with the results of Sadeghi, Cheaib, and Setser [J. Chem. Phys. 90, 219 (1989)] for Ar*. The reactive cross section is appreciably smaller for Kr*(3P0) than for Kr*(3P2). For several reagents, the analysis leads to a preference for formation of KrBr and XeBr in the C state, different from results of flowing afterglow experiments. This points to incomplete correction for collisional relaxation and for overlap of B→X and C→A(3/2) emission in previous work. For most reagents, the vibrational distributions are analogous for both XeBr and KrBr in both the C and B states. For XeBr(B), the results are generally in agreement with the work of Tamagake, Kolts, and Setser [J. Chem. Phys. 74, 4286 (1981)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464546
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  • 3
    Electronic Resource
    Electronic Resource
    The C1s core shake-up spectra of alkene molecules: An experimental and theoretical study (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 6389-6398 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The C1s core photoelectron spectra of a series of alkene molecules, ethene, propene, 1-butene, cis and trans 2-butene, 2-methyl-propene, and 1-pentene are discussed. The experimental spectra are assigned using intermediate neglect of differential overlap-configuration interaction (INDO-CI) calculations and comparative discussions. It is shown that hyperconjugation is a useful concept in the assignment of the transitions. INDO-CI is shown to give a reasonable description of the low energy part of the spectra. The results are used in the discussion of molecular models for the interpretation of the electronic structure of polyacetylene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462633
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  • 4
    Electronic Resource
    Electronic Resource
    Subpicosecond transient infrared spectroscopy of adsorbates. Vibrational dynamics of CO/Pt(111) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 5403-5418 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational dynamics of excited CO layers on Pt(111) were studied using infrared (IR) pump–probe methods. Resonant IR pulses of 0.7 ps duration strongly pumped the absorption line (ν≈2106 cm−1 ) of top-site CO. Weak probe pulses delayed a time tD after the pump were reflected from the CO-covered Pt(111) surface, and dispersed in a monochromator to determine the absorption spectrum of the vibrationally excited CO band, with time resolution 〈1 ps and monochromator resolution 〈1 cm−1. Transient spectra were obtained as a function of CO coverage, surface temperature, and laser fluence. Complex spectra for tD〈0 show features characteristic of a perturbed free induction decay, which are expected based on multiple-level density-matrix models. For tD≥0, the CO/Pt absorption exhibits a shift to lower frequency and an asymmetric broadening which are strongly dependent on fluence (1.3–15 mJ/cm2 ). Spectra return to equilibrium (unexcited) values within a few picoseconds. These transient spectral shifts and the time scale for relaxation do not depend (within experimental error) on coverage for 0.1≤aitch-thetaCO≤0.5 ML or on temperature for 150≤Ts≤300 K. A model for coupled anharmonic oscillators qualitatively explains the tD〉0 spectra in terms of a population-dependent decrease in frequency of the one-phonon band, as opposed to a transition involving a true CO(v=2) two-phonon bound state. The rapid relaxation time and its insensitivity to Ts and aitch-thetaCO are consistent with electron–hole pair generation as the dominant decay mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461657
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  • 5
    Electronic Resource
    Electronic Resource
    Overtone-excited HN3(X˜ 1A'): Anharmonic resonance, homogeneous linewidths, and dissociation rates (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2782-2789 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-resolution spectra have been obtained for the predissociative N–H stretching overtone levels 5ν1 (15 120 cm−1) and 6ν1 (17 670 cm−1) of HN3, cooled in a free-jet expansion. The spectral bandwidth (Doppler limited at 0.007 cm−1 full width at half-maximum (FWHM) is sufficiently narrow to reveal the homogeneous linewidths of individual rovibrational transitions in the 6ν1 band, for which we previously measured the dissociation lifetime in time-domain experiments. Two distinct manifestations of vibrational coupling characterize the spectra: (a) anharmonic mixing of the N–H stretch with other vibrational motions to give a complex spectrum of vibrational eigenstates and (b) homogeneous widths of the resultant states determined by the dissociation lifetime. The results are discussed with reference to previous studies of overtone spectroscopy and intramolecular mixing. Time-domain measurements of dissociation rates are reported for four vibrational levels with zero-order labels 5ν1 +νx. Over the range 15 100 cm−1–17 700 cm−1, the dissociation rate increases monotonically with vibrational energy, with no apparent "mode-specific'' variations. This is interpreted in terms of the highly mixed character of any particular vibrational eigenstate that is excited.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457924
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  • 6
    Electronic Resource
    Electronic Resource
    Nuclear hyperfine structure in the electronic spectrum of propynal (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 187-196 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The laser-induced fluorescence spectrum of propynal (S1←S0) (A˜ 1A‘←X˜ 1A') has been investigated and a series of perturbations due to singlet–triplet coupling resolved. The singlet–triplet interaction matrix elements are of the order of 280 MHz. Fluorescence decays for both the mixed singlet–triplet eigenstates have been measured and are shown to contain quantum beats due to coherent excitation of nuclear hyperfine levels. This Doppler-free measurement in the time domain leads to an accurate determination of the nuclear hyperfine splittings produced by the two nonequivalent hydrogen atoms. The hyperfine structure has been analyzed for two rotational levels in the 91 vibrational state and gives the following values for combinations of the Fermi contact constants and dipole–dipole constants of the two protons in the pure triplet state: T1(a˜ 3A‘): A(1)FC+ 1/2 (T(1)xx−T(1)yy) ∼46 MHz; A(2)FC+ 1/2 (T(2)xx−T(2)yy) −4 MHz; T(1)zz∼T(2)zz ∼0 MHz. A simple model for the spin distribution in propynal predicts that the Fermi contact constant should be positive for the aldehydic proton and smaller and negative for the acetylenic proton and suggests that the Fermi contact constants make the dominant contribution to the effective hyperfine constants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458461
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  • 7
    Electronic Resource
    Electronic Resource
    Spin–orbit distortion of the hyperfine structure in heavier molecules: Breakdown of the case (aβ) formalism in the B 3Φ–X 3Δ system of gaseous NbN (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 1-12 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A detailed analysis of the rotational and hyperfine structure of the (0,0) band of the B 3Φ–X 3Δ electronic transition of NbN has been performed from sub-Doppler spectra taken with linewidths of about 50 MHz. The Nb hyperfine structure is impressively wide in both states, but particularly so in X 3Δ where one of the unpaired electrons occupies a σ orbital derived from the metal 5s orbital. The electron spin and hyperfine structures do not follow the expected case (aβ ) coupling because of extensive second order spin-orbit effects. It is shown that the asymmetry in the spin–orbit structure of X 3Δ is explained almost quantitatively by interaction with a 1 Δ state from the same electron configuration (which lies at 5197 cm−1); also cross terms between the spin–orbit and Fermi contact interactions in the matrix element 〈3Δ2||H||1Δ〉 produce a large correction to the apparent coefficient of the I⋅L magnetic hyperfine interaction in X 3Δ2. The hyperfine structure in a triplet state turns out to be extremely sensitive to the details of the electron spin coupling, and reversals in the sense of the hyperfine structure in the 3Φ4–3Δ3 and 3Φ2–3Δ1 subbands are shown to be consistent with the3Δ state being a regular spin–orbit multiplet (A〉0). Particular care has been taken with the calibration, which has meant that extra terms have needed to be added to the magnetic hyperfine Hamiltonian to account for the spin–orbit distortions: instead of the usual three parameters needed in case (aβ ) coupling, the B 3Φ state has required four parameters and the X 3Δ state has required five. The model explains the data very well, and the standard deviation in the least-squares fit to more than 1000 hyperfine line frequencies was 0.000 58 cm−1 (17 MHz).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457505
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  • 8
    Electronic Resource
    Electronic Resource
    Unimolecular dynamics following vibrational overtone excitation of HN3 v1=5 and v1=6: HN3(X˜;v,J,K)→HN(X 3Σ−;v,J,Ω)+N2 (X 1Σ+g) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 608-609 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Excitation of the NH-stretch overtone transitions of HN3 to v1=5 and 6 resulted in predissociation to HN(X) and N2(X) with lifetimes of 80+60−30 and ≤3 ns, respectively. Following excitation of either overtone, the HN fragments were formed predominantly in the symmetric F1, F3 spin–rotation states, with less than 4% population in the antisymmetric F2 levels. Fragment Doppler profiles confirmed that most of the available energy (〉96%) went into translational motion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455454
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  • 9
    Electronic Resource
    Electronic Resource
    Measurements of two-photon absorption cross sections for liquid benzene and methyl benzenes (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4671-4677 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two-photon cross sections of neat benzene and methyl substituted benzenes at various wavelengths for selective excitation were measured by two-photon induced fluorescence spectra for the first time. The results show that the two-photon rate increases rapidly with the frequency of the photon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453781
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  • 10
    Electronic Resource
    Electronic Resource
    Optical spectra and crystal-field analysis of europium double nitrates (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 5650-5658 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Locations and assignments of crystal-field levels in low-temperature spectra are reported for Eu3+ in the europium double nitrate system [Eu2M3(NO3)12⋅24H2O with M=Mg, Zn]. These energy levels are assigned from the polarized luminescence and the polarized absorption measurements on single crystals at 77 K. The arrangement of the oxygen atoms around the europium ion has approximate icosahedral symmetry and we have tried to find out whether the spectroscopic properties of Eu2M3(NO3)12⋅24H2O reflects this pseudosymmetry, even though the site symmetry of the europium ion is C3. Quantitative crystal-field calculations have first been performed assuming a C3v symmetry which is close to icosahedral. The levels are analyzed in terms of 20 free-ion and 6 crystal-field parameters. Afterwards it is examined how far the C3v parameters can be used to approximate the C3 symmetry. In this case, three additional imaginary crystal-field parameters are taken into account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462664
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