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  • 1
    Digitale Medien
    Digitale Medien
    Photodissociation of CH2. I. Potential energy surfaces of the dissociation into CH and H (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 8240-8249 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The photodissociation processes of CH2 into CH and H have been studied using ab initio multireference configuration-interaction methods. Two-dimensional potential energy surfaces of the ten lowest triplet states correlating with the seven lowest states of CH have been calculated as functions of bond angle and one C–H bond distance, keeping the other C–H distance fixed at the equilibrium CH2 value. Transition dipole moments connecting the excited states with the ground state have been obtained as well. It is shown that efficient photodissociation of CH2 into CH (X 2Π)+H can occur by absorption from the ground X˜ 3B1 (1 3A‘) state into the 1 3A1 (1 3A') state at about 6.3 eV. Photodissociation into excited CH (a 4Σ−)+H can take place through the 1 3A2 (2 3A‘) and 2 3B1 (3 3A‘) states, although in a more complex manner since several avoided crossings occur along the reaction path. The 1 3A2 state is a so-called low-angle state, which has an equilibrium bond angle of less than 60° and correlates directly with C(3P)+H2. At 180°, when the molecule has D∞h or C∞v symmetry, interesting crossings between the ground and low-lying surfaces are found. Altogether, these crossings and correlations are predicted to lead to complicated dissociation dynamics for most of the states. The higher-lying states of CH2 can photodissociate either directly into excited states of CH, or they can be predissociated by the repulsive 1 5A2 (1 5A‘) state, which correlates with CH (a 4Σ−)+H.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.463395
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  • 2
    Digitale Medien
    Digitale Medien
    Theoretical spectroscopy of the NO radical. III. Λ doubling and predissociation in the C 2Π state (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3613-3618 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The Λ doubling of the C 2Π state of NO is calculated by considering the heterogeneous couplings (spin–orbit and rotational angular momentum) between the C 2Π and the first three 2Σ+ states plus the homogeneous interaction of the C 2Π with the B 2Π state. All wave functions and energies result from highly correlated configuration interaction wave functions. A transformation from the adiabatic to the diabatic basis is performed by employing the radial coupling between the two 2Π states. The perturbation matrix is solved in the diabatic basis and leads directly to the eigenvectors and eigenvalues of the Λ components. It is found that for J≥3/2 the Λ components are completely mixed and can therefore not be labeled according to their Ω values any more. Vibrational averaging leads to a calculated value of 0.019 cm−1 (J=0.5, v=0) compared to the measured value of 0.016 cm−1 for the Λ doubling. The predissociation process of the C 2Π state is calculated in the adiabatic basis; the mechanism is found to be caused solely by the spin–orbit interaction with the a 4Π state.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.458577
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  • 3
    Digitale Medien
    Digitale Medien
    Study of the LiZn excimer: Blue–green bands (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7364-7371 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We performed a study of the LiZn excimer formed in the photochemical reaction of Li2(C 1Πu) with Zn(4 1S0). The Li2(C 1Πu) molecules were prepared by excitation with either a dye laser in the region from 348 to 377 nm or an excimer laser at 308 nm. We observed bound–free emission of LiZn at 477 nm. Nonrelativistic ab initio calculations of the potential energy curves and the relevant dipole transition moments have been performed. Using these results in spectral simulations the observed emission is interpreted as belonging to the 2 2Π–X 2Σ+ transition of the LiZn molecule.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.462439
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  • 4
    Digitale Medien
    Digitale Medien
    Resonances and bound rovibrational levels in the interacting X, A, C, and D states of HeH, HeD, 3HeH, and 3HeD (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4369-4383 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Potential energy curves are calculated for the ten lowest states in HeH which correlate with the hydrogen asymptote in the n=1, 2, 3 occupation; these are X, A, C, D, 5 2Σ+, 6 2Σ+, and B, E, 3 2Π as well as the 1 2Δ states. Multireference configuration interaction calculations are employed thereby in an atomic orbital (AO) basis of contracted Gaussians. Extensive calculations of the ∂/∂R, ∂2/∂R2, Lx, and L2 matrix elements are carried out to account explicitly for the effects beyond the Born–Oppenheimer approximation. The positions of rovibrational levels are thereby determined in pairwise close-coupling calculations for the X/A and C/D states of 2Σ+ symmetry for the four isotopomers 4HeH, 3HeH, 4HeD, and 3HeD. Radial, angular, and mass polarization corrections affect the A and C states differently, so that the A–C energy gap increases by 39 cm−1 in 3HeD and by 53 cm−1 in HeH upon introduction of these terms, e.g., whereby the contribution of the mass polarization is by far the smallest. By employing a two-parameter correction function to the calculated electronic potential energy and making use of the calculated non-Born–Oppenheimer terms, a large number of levels for the A, C, and D states as a function of (v,J) quantum numbers are computed which agree with those, which are experimentally available for the C–A and D–A transitions within wave number accuracy.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.460624
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  • 5
    Digitale Medien
    Digitale Medien
    An ab initio potential energy surface for the study of rotationally inelastic OH–H2 collisions (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 3836-3846 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A new two-configuration self-consistent field (SCF) plus dispersion potential for the interaction of OH with H2 is presented. The ground state of OH is a 2Π state leading to a two component potential which is diagonal in the adiabatic electronic basis in which the quantum chemical calculations are done. The transformation between the adiabatic basis and the electronic basis used in collision calculations is described. The transformed potential matrix is Hermitian in this electronic basis when OH–H2 configurations with no plane of symmetry are considered. The orientation dependence of the elements of the potential matrix is given in the form of a spherical expansion and the results are compared with previous potential calculations. The comparison is discussed in terms of the dependence on the orientation of the H2 molecule.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.466130
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  • 6
    Digitale Medien
    Digitale Medien
    Photodissociation of CH2. II. Three-dimensional wave packet calculations on dissociation through the first excited triplet state (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 228-236 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Quantitative results on photodissociation of CH2(X˜ 3B1) through the first excited (1 3A1) triplet state, producing CH (X 2Π)+H(2S), are presented. A three-dimensional time dependent quantum mechanical method was adopted to perform the dynamics using ab initio potential energy surfaces and an ab initio transition dipole moment function. The calculations were performed for J=0, where J is the angular momentum associated with the overall rotation of the nuclei. Comparison with calculations in which the bending angle was kept fixed at its ground state equilibrium value shows that a two-dimensional treatment suffices for obtaining the absorption spectrum. On the other hand, a three-dimensional calculation is necessary for correctly predicting the final rotational state distribution of the CH fragment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.465800
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  • 7
    Digitale Medien
    Digitale Medien
    The NaZn excimer: Blue–green band (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 4672-4679 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Electronically excited NaZn excimers have been produced in a photochemical reaction of Na2(C 1Πu) with Zn(4 1S0). The Na–Zn vapor mixture was prepared by introducing a controlled stream of sodium vapor into zinc vapor generated in a heat-pipe oven. A new band (bound–free transition) was observed in the region from 450 to 487 nm. Potential curves of the eight lowest electronic states of NaZn were calculated. On the basis of the calculations, the observed emission is interpreted as resulting from the 2 2Π–X 2Σ+ transition. The conditions favorable for the observation of the photochemical reaction are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.464971
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  • 8
    Digitale Medien
    Digitale Medien
    Photodissociation of CH2. III. Two-dimensional dynamics of the dissociation of CH2, CD2, and CHD through the first excited triplet state (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1113-1127 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We present quantitative results on photodissociation of CH2 (X˜ 3B1) and its isotopomers CHD and CD2 through the first excited triplet state (1 3A1). A two-dimensional wave packet method employing the light–heavy–light approximation was used to perform the dynamics. The potential energy surfaces and the transition dipole moment function used were all taken from ab initio calculations. The peak positions in the calculated CH2 and CD2 spectra nearly coincide with the positions of unassigned peaks in experimental CH2 and CD2 3+1 resonance enhanced multiphoton ionization spectra, provided that the experimental peaks are interpreted as two-photon transitions. Comparing the photodissociation of CH2 and its isotopomers to photodissociation of water in the first absorption band, we find these processes to be very similar in all aspects discussed in this work. These aspects include the origin of the diffuse structure and the overall shape of the total absorption spectra of vibrationless and vibrationally excited CH2 , trends seen in the fragment vibrational level distribution of the different isotopomers, and selectivity of photodissociation of both vibrationless and vibrationally excited CHD. In particular, we find that the CD/CH branching ratio exceeds two for all wavelengths in photodissociation of vibrationless CHD.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.466643
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  • 9
    Digitale Medien
    Digitale Medien
    Photodissociation of CH2. V. Three-dimensional adiabatic potential energy surfaces and transition dipole moments (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8930-8941 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Full three-dimensional adiabatic potential energy surfaces are presented for the lowest five 3A‘ and five 3A' states of CH2. Both the 1 3A' and 2 3A‘ states are dissociative with respect to the C–H coordinates, consistent with our earlier two-dimensional results. All higher lying states are found to be bound for this coordinate, although the barrier toward dissociation is small for some states. In terms of angle dependence, the 1 3A' state shows a flat behavior, but tends towards larger angles as dissociation proceeds. Most excited 3A' states are somewhat bent with only a small barrier to linearity. Transition dipole moments connecting the ground state with the excited triplet states are presented as well. The 1 3A' state is the only state of that symmetry with a large transition dipole moment in the Franck–Condon region. Other 3A' states exhibit large values only if one bond is stretched compared with the ground state equilibrium geometry. The 1 3A‘, 3 3A‘, and 4 3A‘ states are also slightly bent with a small barrier to linearity. However, the 2 3A‘ state has an absolute minimum at very small angles (less than 60°), and shows a considerable local minimum (∼1.5 eV) for the linear configuration. The 5 3A‘ state prefers the linear shape. The 3 3A‘ state has the largest transition dipole moment function in the Franck–Condon region, but the transition moments to other 3A‘ states can exhibit large values outside this region. The 2 3A‘ and 3 3A‘ states undergo an avoided crossing in the Franck–Condon region, so that a coupled states treatment is necessary for a correct description of the photodissociation dynamics. In order to provide the corresponding transition dipole moments in an appropriate form, a transformation to the principal axes of inertia was performed. The adopted transformations are discussed in detail. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.468947
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  • 10
    Digitale Medien
    Digitale Medien
    Ab initio calculations of the spin–orbit splitting in the C˜ state of CF4+ including the dynamical Jahn-Teller effect (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 4124-4131 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Detailed ab initio calculations on the lowest vibrational state of the electronic C˜ 2T2 manifold of CF4+ show a small Jahn-Teller effect in all asymmetric modes. This results in only small distortions from tetrahedral symmetry, but due to strong coupling between electronic and nuclear motions (dynamical Jahn-Teller effect), the spin–orbit splitting is reduced by an order of magnitude. This answers the outstanding question on the large differences between the results of electronic structure calculations and measurements on spin-orbit splittings in XY4 molecules or molecular ions [R. N. Dixon and R. P. Tuckett, Chem. Phys. Lett. 140, 553 (1987); J. F. M. Aarts and J. H. Callomon, Mol. Phys. 81, 1383 (1994)]. Complete agreement with experiment is however not reached because the dynamical Jahn-Teller effect is very sensitive to small errors in the potential energy surface. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.480961
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