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  • 1
    Electronic Resource
    Electronic Resource
    Photodissociation dynamics and emission spectroscopy of H2S in its first absorption band: A time dependent quantum mechanical study (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6520-6534 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical study of the photodissociation dynamics of H2S in its first absorption band is presented. The potential energy surfaces underlying the dynamics of the breakup process have been modeled so as to reproduce the principal features of all the available experimental data. The modeling is performed using time dependent quantum dynamical methods and involves the exact numerical solution of the time dependent Schrödinger equation. The fitting of the experimental observations requires the use of potential energy surfaces corresponding to two excited electronic states. We have been able to determine two such surfaces which reproduce the observed structure in the absorption spectrum, the main features of the emission spectrum of the dissociating molecule, and the vibrational distribution of the HS photofragments. The calculations utilize a recently developed method for analyzing the wave packet dynamics to extract the partial photodissociation cross sections. The photodissociation process is found to be consistent with an initial excitation to a single excited dissociative diabatic electronic state which is weakly coupled to another, whose principal role within the first absorption band is to introduce diffuse structure into the absorption spectrum and minor perturbations to the nuclear motion. The motion on the principal dissociative electronic surface is dominated by that in the two bond stretching coordinates, while that on the surface of the second perturbing state is a one dimensional vibrational motion which may correspond to either symmetric stretching or bending, but is most probably a complex combination of both. A new method is presented for performing the time dependent quantum mechanical calculation on two coupled potential energy surfaces when the motions on both surfaces are treated in a reduced dimensionality and the dynamically active coordinates on the two surfaces are different.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459678
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamical and stereochemical aspects of photodissociation (1991)
    s.l. : American Chemical Society
    Accounts of chemical research 24 (1991), S. 16-21 
    Details
    ISSN: 1520-4898
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ar00001a003
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  • 3
    Electronic Resource
    Electronic Resource
    Photodissociation dynamics of A˜ state ammonia molecules. II. The isotopic dependence for partially and fully deuterated isotopomers (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 6472-6481 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The technique of H(D) Rydberg atom photofragment translational spectroscopy has been used to investigate the photodissociation dynamics of the mixed isotopomers NH2D and NHD2 following the excitation to the v2′=0 and 1 levels of their lowest lying A˜ 1B1 (C2v) excited electronic states. Peaks in the resulting total kinetic energy release (TKER) spectra are assigned to levels of the NH2, NHD, or ND2 fragments with a wide range of quantum numbers Ka for rotation about their a inertial axes, and with N=Ka, N=Ka+1, or N=Ka+2 as appropriate. These data provide the first measurements of high rotational levels for the ground electronic state of the NHD radical. The least squares fitting of all these spectra, and those resulting from NH3 and ND3, to the best calculated NH2, NHD, and/or ND2 rotational term values provides accurate estimations of the respective N–H and N–D bond dissociation energies D00 across the whole series. These values are D00(H–NH2)=37 115±20 cm−1 (4.602±0.002 eV); D00(H–NHD)=37 240±50 cm−1; D00(H–ND2)=37 300±30 cm−1; D00(D–NHD)=37 880±60 cm−1; and D00(D–ND2)=38 010±20 cm−1. The differences between these values are fully consistent with differences in zero-point energies and lead to a mean value of De=40 510±25 cm−1. Dissociation of NH2D or NHD2 through their (A˜−X˜) 210 bands to give an NHD product leads to TKER spectra with a much higher statistical character than those leading to an NH2 or ND2 product, and to those obtained following excitation through the 000 bands. This is rationalized in a semiquantitative manner in terms of a varying contribution to the dissociation rate of the parent molecules from internal conversion (IC) to high levels of their respective ground states. Nuclear permutation symmetry appears to play an important role both for the IC rates and for the subsequent branching between product channels. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471368
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  • 4
    Electronic Resource
    Electronic Resource
    Near ultraviolet photolysis of methanethiol studied by H atom photofragment translational spectroscopy (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 7538-7547 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The technique of H Rydberg atom photofragment translational spectroscopy has been applied to a high resolution study of the primary photochemistry of methanethiol (CH3SH) following excitation at a wide range of wavelengths in the near ultraviolet. In accord with previous studies of this molecule, excitation within its first (1 1A‘−X˜ 1A') absorption continuum is shown to result in S–H bond fission. Spectral analysis yields a refined value for the bond dissociation energy: D00(CH3S–H)=30 250±100 cm−1. The resulting CH3S(X˜) fragments are deduced to carry only modest vibrational excitation, distributed specifically in the ν3 (C–S stretching) mode and in one other mode having a wave number of ∼1040 cm−1. We associate this latter mode with bending of the CH3 moiety in the plane containing the C and S nuclei and the lobe of the unpaired electron which was originally involved in the S–H bond. Decreasing the excitation wavelength (while remaining within the first absorption continuum) results in an increase in both the vibrational and rotational excitation of the CH3S(X˜) fragments, but a decrease in the relative yield of the upper (2E1/2) spin–orbit component. Excitation at still shorter excitation wavelengths accesses the second (2 1A‘−X˜ 1A') absorption band of CH3SH. The CH3S fragments resulting from S–H bond fission at these excitation wavelengths are observed to carry very much higher levels of vibrational excitation in the above two modes. The observation of H atoms attributable to secondary photolysis of SH(X) fragments indicates increased competition from the alternative C–S bond fission channel at these shorter excitation wavelengths. Additional peaks in the H atom time-of-flight spectrum, most clearly evident following excitation at wavelengths in the range 213–220 nm, are interpretable in terms of secondary photolysis of the primary CH3S(X˜) fragments yielding thioformaldehyde (H2CS), primarily in its A˜ 1A2 excited electronic state. Symmetry arguments provide an explanation for this specific electronic branching in the near ultraviolet photolysis of CH3S fragments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468248
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  • 5
    Electronic Resource
    Electronic Resource
    The heats of formation of HNO and of DNO (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 6905-6906 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The heat of formation ΔfHo (0 K) of HNO, deduced from spectroscopic measurements, is 110.02±0.25 kJ mol−1; and for DNO is 106.85±0.25 kJ mol−1. ©1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471714
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  • 6
    Electronic Resource
    Electronic Resource
    Resonance enhanced multiphoton ionization spectroscopy of the SnF radical (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 4406-4410 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The resonance enhanced multiphoton ionization spectrum of the free radical SnF has been recorded using excitation wavelengths in the range 540 to 360 nm. The previously documented C 2Δ, D, E 2Π, and F 2Σ+ states and two hitherto unidentified excited states, the H and I 2Φ states, were all observed as two-photon resonances. Band contour simulations yielded spectroscopic constants for the E, F, and I states. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471192
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  • 7
    Electronic Resource
    Electronic Resource
    Λ-doublet and spin-doublet population distributions in the products of photofragmentation via coupled electronic channels: H2O(B˜ 1A1)→H+OH(X 2Π) (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 301-309 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The consequences of the photofragmentation of a triatomic molecule on several coupled potential energy surfaces are considered with specific attention to branching ratios over the fine structure components of an open-shell product with orbital degeneracy. Attention is limited to the cases where the parent molecule dissociates on singlet surfaces. It is shown how the components of the outgoing wave function on the different surfaces interfere in determining these ratios. The theory is applied to the dissociation of H2O through its second B˜ 1A1 excited state, for which the coupling between three singlet states of the parent (B˜, A˜, and X˜) leads to two sets of dissociation products, H+OH(X 2Π) and H+OH(A 2Σ+). The variation with N of the Λ-doublet ratios in the OH(X) state is found to be a very sensitive function of the quantum state of the parent molecule, of the energy, and of the exit channel potentials. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469403
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  • 8
    Electronic Resource
    Electronic Resource
    Photodissociation dynamics of A˜ state ammonia molecules. I. State dependent μ-v correlations in the NH2(ND2) products (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 6460-6471 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The H(D) Rydberg atom photofragment translational spectroscopy technique has been applied to a further detailed investigation of the photodissociation dynamics of NH3 and ND3 molecules following excitation to the lowest two (v2=0 and 1) vibrational levels of the first excited (A˜ 1A2″) singlet electronic state. Analysis of the respective total kinetic energy release spectra, recorded at a number of scattering angles aitch-theta [where aitch-theta is the angle between the ε vector of the photolysis photon and the time-of-flight (TOF) axis], enables quantification of a striking, quantum state dependent, μ-v correlation in the NH2(ND2) products. The spatial distribution of the total flux of H(D) atom photofragments is rather isotropic (βlab∼0). However, more careful analysis of the way in which the TOF spectra of the H(D) atom photofragments vary with aitch-theta reveals that each H+NH2(D+ND2) product channel has a different "partial'' anisotropy parameter, βlab(v2,N), associated with it: The H(D) atom ejected by those molecules that dissociate to yield NH2(ND2) fragments with little rotational excitation largely appear in the plane of the excited molecule (i.e., perpendicular to the transition moment and the C3 axis of the parent, with β tending towards −1). Conversely, the H(D) atoms formed in association with the most highly rotationally excited partner NH2(ND2) fragments tend to recoil almost parallel to this C3 axis (i.e., β→+2). Such behavior is rationalized in the context of the known potential energy surfaces of the A˜ and X˜ states of ammonia using a classical, energy and angular momentum conserving impact parameter model in which we assume that all of the product angular momentum is established at the "point'' of the conical intersection in the H–NH2(D–ND2) dissociation coordinate. We conclude by reemphasizing the level of care needed in interpreting experimentally measured β parameters in situations where there is averaging over either the initial (parent) or final (product) quantum states. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471367
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  • 9
    Electronic Resource
    Electronic Resource
    Observation of a parallel recoil distribution from a perpendicular absorption transition in formyl radicals HCO and DCO (1991)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 8013-8018 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100174a006
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  • 10
    Electronic Resource
    Electronic Resource
    State to state recoil anisotropies in the photodissociation of deuterated ammonia (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 7659-7662 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The near ultraviolet photodissociation of deuterated ammonia, ND3, allows particularly clear observation and quantification of the quantum state dependent angular anisotropy of the recoiling D+ND2(X˜) photoproducts. The recoil anisotropy is shown to depend upon five quantum numbers: The rotational quantum numbers of the parent molecule selected in the absorption process, and the rotational and vibrational quantum numbers of the resulting products. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477411
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