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  • 1
    Electronic Resource
    Electronic Resource
    Quantum and Molecular Mechanics Study of the Tris(Quaternary Ammonium) Cation Used as the Zeolite ZSM-18 Synthesis Template (1994)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 12911-12918 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100100a017
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  • 2
    Electronic Resource
    Electronic Resource
    Multidimensional dynamics in the electron stimulated desorption of ammonia from Pt(111) (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6318-6329 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We characterize the electron stimulated desorption of neutral ammonia (NH3 and ND3) from Pt(111) with vibrational and rotational quantum resolution by using (2+1) resonance enhanced multiphoton ionization detection. Two significant isotope effects appear: (1) the desorption yield of NH3 is three times that of ND3 and (2) NH3 desorbs with considerably more "spinning'' rotational energy than does ND3. We find virtually identical translational energy distributions for each desorbate and roughly equal vibrational energy distributions. Vibrational excitation is found exclusively in the ν2 symmetric deformation or "umbrella'' mode, independent of isotope. These effects cannot be explained by desorption induced by vibrational energy transfer. Instead, desorption is the result of excitation of a 3a1 electron principally on the N atom, which causes the pyramidal NH3 adsorbate to rapidly invert. Ab initio calculations of two-dimensional potential energy surfaces (intramolecular bond angle and surface bond length) reveal that near-inverted molecules deexcite to a repulsive hard wall of the adsorbate–substrate interaction and desorb. Spinning excitation derives from the rotational barrier of the inverted molecule. Both isotope effects are direct consequences of desorption via inversion. In general, multidimensional dynamics must be considered in the study of stimulated surface processes. Our calculations also indicate that excited-state forces at equilibrium molecule–surface distances are an order of magnitude less than those derived from a currently accepted image-potential model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468385
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  • 3
    Electronic Resource
    Electronic Resource
    Photochemistry of adsorbed molecules. XV. Localized atomic scattering in the photolysis of HI/LiF(001) and HI/NaF(001) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 5005-5019 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have compared the "elastic'' H atom angular-scattering, Pel(θ′), of HI(ad) photolyzed at 248 nm for LiF and NaF substrates, both experimentally and theoretically. The observed Pel(θ′) for elastic scattering were similar for LiF and NaF, with a peak in the range 43°–48°. The Pel(θ′) for H from HI/NaF was broader than that for H from HI/LiF. Energy distributions, P(ET′), for H recoiling from HI/LiF and HI/NaF are also reported. A semiempirical potential-energy surface (pes) is given for HI adsorbed on NaF, based on an earlier one for LiF [J. Chem. Phys. 94, 978 (1991)]. Ab initio "density function theory'' (DFT) calculations were performed to verify the suitability of this pes; the DFT points were in satisfactory agreement with the semiempirical pes. For HI/LiF the DFT calculation gave a heat of adsorption of about 9 kcal/mol, the semiempirical model gave 5 kcal/mol, and experiment gave 7 kcal/mol. We have computed H atom scattering by the classical trajectory method for two different models one involving dense and the other perforated arrangements of the HI adsorbate molecules. Comparison with the experimental results showed that the second model gave a better description of both Pel(θ′) and P(ET′) for HI/LiF and HI/NaF. The calculations showed that the angular and energy distributions of the scattered H were sensitive to the size of the vacancies between adjacent adsorbate molecules. The study also indicates the importance of unit-cell size in relation to the size of the adsorbate molecule in determining adsorbate geometry and hence the energy and angular distributions of the scattered photofragments. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472339
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  • 4
    Electronic Resource
    Electronic Resource
    Spectra and structure of organophosphorus compounds. 22. Microwave, infrared and Raman spectra, structure, vibrational assignment and normal-coordinate analysis of methylphosphonothioic difluoride (1983)
    s.l. : American Chemical Society
    Inorganic chemistry 22 (1983), S. 4134-4141 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00168a061
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  • 5
    Electronic Resource
    Electronic Resource
    Spectra and structure of organogermanes. XXII. Microwave, infrared, and Raman spectra of methylgermyl cyanide (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 10-23 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The microwave spectra have been recorded from 18.0 to 26.5 GHz for 12CH3GeH212C14N, 13CH3GeH212C14N, 12CH3GeH212C15N, 12CH3GeH213C14N, 12CH3GeD212C14N, and 12CD3GeH212C14N of the four naturally occurring isotopes of germane: 70Ge, 72Ge, 74Ge, and 76Ge. Only a-type transitions were observed and R-branch assignments have been made for all the isotopic species in the ground vibrational state from which the rotational constants were determined. From these data the complete structural parameters were determined to be r0(CME–Ge)=1.933±0.002 A(ring), r(Ge–CCN)=1.927±0.004 A(ring), r(C≡N)=1.155±0.004 A(ring), r(Ge–H)=1.521±0.001 A(ring), r(C–Hs)=1.092±0.005 A(ring), r(C–Ha)=1.092±0.005 A(ring), (arc left)CGeC=107.36°±0.60°, (arc left)HGeH=111.41°±0.04°, (arc left)HGeCMe=112.92°±0.08°, (arc left)HsCGe=109.5°±2.0°, and 〈HaCGe=109.3°±0.8°, where all of the parameters are rs values except for the carbon–hydrogen distances and angles. The dipole moment components were determined from the Stark effect to be ||μa||=4.20±0.14, ||μb||=0.39±0.03, and ||μt||=4.22±0.14 D. From the microwave splitting method, the threefold barrier to internal rotation was determined to be 1148±23 cal/mol (402±8 cm−1). The infrared (3200 to 50 cm−1) and Raman spectra (3200 to 10 cm−1) of gaseous and solid CH3GeH2CN, CH3GeD2CN, and CD3GeH2CN have been obtained. Additionally, the Raman spectra of the liquids have been recorded and qualitative depolarization values have been obtained. A complete vibrational assignment is proposed based on infrared band contours, depolarization values, and isotopic shifts. These results are compared to similar quantities in some related molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449802
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  • 6
    Electronic Resource
    Electronic Resource
    Spectra and structure of organogermanes. XXIV. Microwave spectra, quadrupole coupling constants, and structure of methylgermyl bromide (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 5796-5809 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The microwave spectra from 26.5 to 39.0 GHz of eighteen isotopic species of methylgermyl bromide, 12CH3GeH2Br, 12CH3GeD2Br, and 13CH3GeH2Br for three of the naturally occurring isotopes of germane, 70Ge, 72Ge, and 74Ge, as well as the two of bromine, 79Br and 81Br, have been measured and assigned. From these data, substitution structural parameters were determined except for the methyl group. The determined parameters are: r(Ge–Br)=2.308±0.002 A(ring), r(Ge–C)=1.933±0.002 A(ring), r(Ge–H)=1.520±0.001 A(ring), r(C–Hs)=1.100±0.012 A(ring), r(C–Ha)=1.097±0.030 A(ring), CGeBr=107.0±0.2°, HGeH=111.5±0.1°, HGeC=112.2±0.1°, GeCHs=110.3±4.7°, and GeCHa=111.9±1.7°. From a diagnostic least-squares adjustment to fit 36 rotational constants, r0 structural parameters were also obtained. Quadrupolar coupling constants have been obtained. These results are compared to similar quantities in some related molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449889
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  • 7
    Electronic Resource
    Electronic Resource
    Spectra and structure of organophosphorus compounds. XXIII. Microwave spectra, electric dipole moment, and molecular structure of two conformers of ethyldifluorophosphine (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 3894-3902 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The microwave spectrum of ethyldifluorophosphine, CH3CH2PF2, has been investigated in the region from 18.0 to 39.5 GHz. The spectra of two conformers have been identified. The ground state and seven vibrationally excited states have been assigned for the more stable gauche conformer (phosphorus lone pair with respect to CH3 group), whereas the ground state and one excited state have been assigned for the trans form. Rotational and most quartic centrifugal distortion constants have been determined with A=6784.501(3), B=2930.156(2), C=2352.576(2) MHz for gauche and A=5444.910(3), B=3290.133(3), C=2871.915(3) MHz for trans, both in the ground state. Electric dipole moments were obtained from ground state Stark effect measurements: || μa||=1.990(4), || μb||=0.855(4), || μc||=0.091(7), || μt||=2.168(2) D for gauche and || μa||=1.780(10), || μb||=0, || μc||=1.077(10), || μt||=2.081(10) D for trans. Using a new computer program, a diagnostic least-squares fit of the structural parameters suggests significant structural differences between the conformers, notably the C–C–P angle which changes from 110.7° in the gauche form to 114.9° in the trans form. From a temperature study of the microwave spectrum, it was found that the gauche conformer is at least 80 cm−1 (229 cal/mol) more stable than the trans conformer. These results are compared to similar quantities in some corresponding molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448880
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  • 8
    Electronic Resource
    Electronic Resource
    Microwave spectrum, conformation, and low frequency vibrational spectrum of cyclopropylisothiocyanate (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3663-3671 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: 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 A(ring),(arc left)CNC=143.8±4.2 °, and (arc left)CCN=118.7±0.1 ° for the trans conformer and r(C–N)=1.414±0.017 A(ring), (arc left)CNC=144.4±1.1, and (arc left)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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450205
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  • 9
    Electronic Resource
    Electronic Resource
    Analysis of torsional spectra of molecules with two internal C3v rotors. XXIII. Microwave, infrared, and Raman spectra, barriers to internal rotation, and vibrational assignment of 3,3,3-trifluoro-2-methylpropene (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1507-1516 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The microwave spectrum of 3,3,3-trifluoro-2-methylpropene, H2C=C(CH3)CF3 has been recorded from 18.5 to 39.0 GHz. Only a-type transitions were observed and R-branch assignments have been made for the ground vibrational state as well as for three vibrational excited states of the CF3 torsion and one excited state of the CH3 torsion. The rotational constants for the ground vibrational state were found to have the following values: A=3549.25±0.35, B=2465.82±0.05, and C=1978.25±0.02 MHz. The dipole moment components were determined from the Stark effect to be ||μa||=2.44±0.01, ||μb||=0.59±0.09, and ||μt||=2.51±0.03 D. From an analysis of the internal rotational splittings, the threefold barrier for the methyl group was found to be 603±19 cm−1 (1.72 kcal/mol). This value is consistent with the value of 610±4 cm−1 (1.74 kcal/mol) obtained from the far infrared spectrum where the fundamental was assigned at 160.9 cm−1, but only if kinetic coupling between the perfluoromethyl and methyl torsion is taken into account. The CF3 torsional mode was observed at 55.9 cm−1 from which a threefold periodic barrier of 743±7 cm−1 (2.12 kcal/mol) was calculated. No appreciable potential coupling was found between the two C3v rotors. The infrared (3500 to 30 cm−1) and Raman spectra (3500 to 10 cm−1) have been recorded for both the gas and solid states. Additionally, the Raman spectrum of the liquid was recorded and qualitative depolarization values were obtained. All of the normal modes have been assigned based on band contours, depolarization values, and group frequencies. These results are compared to the corresponding quantities in some similar molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449387
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  • 10
    Electronic Resource
    Electronic Resource
    Reaction dynamics from liquid structure (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 2458-2464 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The possible connection between the equilibrium structure of a solution and the chemical reaction dynamics that occur in that solution has been discussed by Adelman and co-workers. In this work, we present a computational demonstration of this connection using molecular dynamics simulations and the generalized Langevin equation (GLE). A favorable example of a reaction loosely based on thermally activated Cl+Cl2→Cl2+Cl in argon solvent is used for this demonstration by (1) computing equilibrium solution structural information in terms of the Ar–Ar and Ar–Cl radial distribution functions, both from integral equations and from molecular dynamics; (2) deriving a memory function for Cl in argon solvent from the radial distribution functions and the Ar–Cl potential; and (3) using this memory function in a simple GLE to compute the dynamics of the reaction. Energy flow results both for climbing and descending the barrier are in gratifying agreement with the dynamics of the same reaction as computed by full deterministic molecular dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461802
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