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  • 1
    Electronic Resource
    Electronic Resource
    The F+HD→DF(HF)+H(D) reaction revisited: Quasiclassical trajectory study on an ab initio potential energy surface and comparison with molecular beam experiments (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 9248-9262 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of the F+HD reaction has been studied by means of quasiclassical trajectory calculations on an ab initio potential energy surface (PES) at several collision energies. At the collision energy of 85.9 meV and for the DF+H isotopic channel of the reaction, there is a remarkable agreement between calculated and experimental results, in both the center of mass (c.m.) differential cross sections (DCS) and in the simulation of the laboratory (LAB) time of flight (TOF) and angular distributions (AD). The good agreement also extends to the lower collision energy of 58.6 meV for this channel of the reaction. In contrast, the simulation of the LAB angular distributions for the HF+D channel shows strong discrepancies between theory and experiment at both collision energies, which can be traced back to the absence of a forward peak in the calculated c.m. DCS for HF(v'=3). Simulations made from QCT calculations on other PES with important HF(v'=3) forward scattering contributions also fail to reproduce the overall AD. The theoretical findings and especially the roles of translational energy and initial rotational momentum on the dynamics of this reaction are discussed in terms of the topology of the PES through the analysis of individual trajectories. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468875
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  • 2
    Electronic Resource
    Electronic Resource
    The radiative lifetime of A 1Πu C2 (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2847-2853 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This note reports ab initio potential curves of A 1Πu and X 1Σ+g states of C2, and the A–X radiative lifetimes. The calculations are based upon configuration interaction wave functions formed from single and double electron excitations from state-averaged MC-SCF reference functions expanded in a Gaussian basis. The lifetimes for (J′=1,v′) A 1Πu are calculated to be about 25% longer than those found in previous ab initio works, but about 25% shorter than the most recent LIF measurements of Bauer, Becker, Bielefeld, and Meuser. Also reported are the quadrupole moments of the A 1Πu and X 1Σ+g states as a function of internuclear distance and the quadrupole lifetimes of several (v′=0,J′) levels in the X state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453072
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  • 3
    Electronic Resource
    Electronic Resource
    The ultraviolet absorption spectrum of the A˜ 1A‘2←X˜ 1A1 transition of jet-cooled ammonia (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 6669-6676 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The A˜←X˜ absorption spectra of NH3 and ND3, recorded in a cold molecular jet, are presented. Vibrational band progressions resolvable up to v'2=14 appear. No other vibrations are present, either alone or in combinations. Relative band intensities for v2 progressions are recorded, and the homogeneous lifetime broadenings of vibrational levels of the A˜ state are reported. The FWHM linewidths span 34–293 cm−1 over all bands of NH3 and 30–135 cm−1 over the v'2=2 through 14 bands of ND3. In general, the rate of dissociation increases nonlinearly with vibrational energy. The band intensity alternation, previously observed only in matrix spectra below 15 K, has been observed in these very cold gas phase samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452415
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical A 1A‘2–X 1A1 absorption and emission spectrum of ammonia (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 6677-6692 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy, electric dipole moment, and electronic transition moment surfaces have been calculated for the A and X states of NH3 from CASSCF and CEPA electronic wave functions. Anharmonic vibrational term values, Franck–Condon factors, and A–X radiative transition probabilities for the symmetric stretching and bending modes of NH3 and ND3 have been evaluated. The theoretical absorption spectra at room and low temperatures agree well with experimental data. The symmetric stretching mode in the A state has only small intensities in the A–X absorption spectrum. Emission rates from various initial vibronic levels of the A state are given. The ab initio electric dipole moment surfaces for the ground state of NH3 have been used to compute transition moments, which are in good agreement with experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452416
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  • 5
    Electronic Resource
    Electronic Resource
    Dissociation of NH3 to NH2+H (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 6693-6700 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy, dipole moment, and electronic transition moment surfaces for the lowest dissociative pathways of the singlet X˜ and A˜ states of NH3 yielding NH2 (X˜ 2B1,A˜ 2A1) +H(2S) products have been calculated using complete active space MCSCF ab initio wave functions. The A˜ state dissociation proceeds via a minimum barrier at the following planar geometry: αHNH =113°, rNH =1.042 A(ring) (in the NH2 fragment), and RNH =1.323 A(ring) (in the dissociation coordinate). The barrier height is calculated to be 3226 cm−1 with an expected accuracy of about 300 cm−1. The barrier height increases with increasing out-of-plane angle. Close to the barrier there are strong variations of the shapes of the dipole moment and transition moment surfaces. The minimum energy path through the X˜–A˜ conical intersection follows planar geometries. Along this pathway the angle αHNH decreases, but the distance rNH in the NH2 fragment hardly changes. The crossing distance RcNH of the X˜ and A˜ states in planar structures depends strongly on αHNH and varies from about 1.68 A(ring) (60°) to infinity (180°). The photodissociation process NH3(A˜) →NH2(X˜ 2B1) +H(2S) is discussed on the basis of the calculated potential energy surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452417
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  • 6
    Electronic Resource
    Electronic Resource
    Bound electronic states of HCl− (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 7232-7240 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper reports ab initio Born–Oppenheimer calculations on the X 1Σ state of HCl and on the 1 2Σ, 2 2Σ, and 2Π states of HCl− for internuclear distances at which these states are electronically bound. The calculations employed square-integrable configuration interaction wave functions which included all single and double replacements from multiconfiguration reference functions. The MC-SCF reference configurations and the Gaussian atomic basis encompass the dominant effects which govern the electronic states studied. In the process of these calculations, we have calculated the static polarizability of Cl− and reproduced the known polarizabilities of H, Cl, and H−. The calculations on the X 1Σ state of HCl yield a De within 0.10 eV of the measured value, and ωe within 3 cm−1 of the measured value. For the molecular ion, we find the potential of the 1 2Σ state of HCl− to be attractive and to undergo substantial charge transfer, and the potentials of the 2Π and 2 2Σ states to be repulsive even at large internuclear separations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451360
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  • 7
    Electronic Resource
    Electronic Resource
    An ab initio calculation of the near-equilibrium potential energy surface and vibrational frequencies of H2Br+ and its isotopomers (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 1683-1686 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The near-equilibrium potential energy surface of H2Br+ was calculated by SCEP-CEPA using a basis set of 82 contracted GTOs. The equilibrium geometry is predicted to be re=1.441 A(ring) and αe=92.1°. Vibrational frequencies were calculated variationally and the fundamentals of H279Br+ (in cm−1) are ν1=2403, ν2=1073, and ν3=2398. An unusual isotopic effect, due to vibrational anharmonicity, is discussed. The calculated proton affinity of HBr of 587 kJ mol−1 is in excellent agreement with experimental values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450465
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  • 8
    Electronic Resource
    Electronic Resource
    Ab initio calculation of potential energy surfaces and spectroscopic properties of H2S and H3S+ (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5107-5116 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy surfaces and spectroscopic properties were calculated for H2S and H3S+ from highly correlated SCEP-CEPA wave functions. The equilibrium geometry of H3S+ is predicted to be re =1.350 A(ring) and θe =32.2°. The vibrational frequencies of H323S+ (in cm−1) were calculated to be 2529 (ν1), 1050 (ν2), 2527 (ν3), and 1208 (ν4) which are all in close agreement with experimental values obtained for solid H3S+SbF−6. The computed proton affinity for H2S of PA298=716.7 kJ mol−1 is in very good agreement with experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451703
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  • 9
    Electronic Resource
    Electronic Resource
    Vibrational relaxation of N2 by collision with He atoms (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3788-3797 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A quantum mechanical study of vibrational relaxation in the collision of N2 with 3He and 4He is reported. An ab initio potential energy surface has been computed using the coupled electron pair approximation with an extended basis set. Cross sections for v=1 → 0 vibrational relaxation have been calculated on this surface by using the centrifugal sudden approximation (CSA). The calculated vibrational relaxation rate coefficients show a very encouraging agreement with those measured in laser fluorescence experiments for the temperature range 82–291 K. Over this temperature range the rate coefficients increase by a factor close to 100. The CSA computations are also used to test the accuracy of the vibrational close coupling, rotational infinite order sudden, and the breathing sphere approximations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450089
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  • 10
    Electronic Resource
    Electronic Resource
    Bent valence excited states of CO2 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 8382-8388 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The conical intersection regions on the potential energy functions of the valence excited 1,3Σu−, 1,3Δu, 3Σu+, and 1,3Πg states of CO2 have been investigated by ab initio calculations. Using large scale multireference configuration interaction the ordering of the lowest valence excited states of CO2 has been calculated to be 3B2, 3A2, 1A2 followed by 1B2. All these states have bent equilibrium structures and lie energetically below their dissociation asymptotes. The near equilibrium parts of the potential energy functions have been mapped in three dimensions by multiconfiguration self-consistent field calculations. The 1,3B2 and 1,3A2 states differ in their equilibrium angles (118° and 127°, respectively), and have much longer equilibrium distances (around 1.26 A(ring)) than the electronic ground state. Anomalously low values of ca. 800 cm−1 have been calculated for the wave number of the antisymmetric stretching vibrations of the 1A2, 3B2, and 1B2 states. The crossings between the bent valence excited states in the geometry region 90°≤αOCO≤150° and 1.1 A(ring)≤RCO≤1.4 A(ring) have been located.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463408
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