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  • 1
    Electronic Resource
    Electronic Resource
    Emission spectra and electronic structure of group IIIa monohalide cations (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 7112-7125 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Optical spectra of ten AX+ ions (A=B, Al, Ga, In; X=F, Cl, Br) have been observed in the visible and near UV; a total of 18 band systems were newly discovered. The emission was produced by chemiluminescent reactions A++X2 at low (2–10 eVCM) kinetic energy in a beam-gas arrangement. A position-sensitive photon counting detector with large surface area and very low dark count rate was employed, the resolution was mostly 5–50 A(ring) FWHM. Three types of band systems were observed: (1) For all AX+ combinations except BCl+ and BBr+, a very broad quasicontinuum with undulatory structure appears. On the basis of electronic state correlation arguments, photoelectron data, some ab initio calculations and, in one case, a known emission spectrum (InCl+) these band systems were identified as B 2Σ+–X 2Σ+ transitions. It is concluded that the excited state potentials are considerably displaced against the ground state, and their energetics are given. (2) For six species AX+, narrow band systems were observed in the 2500 A(ring) region. They could be clearly identified as being due to C 2Π–X 2Σ+ transitions by means of comparison with the systematics of the analogous A 2Π–X 2Σ+ transitions of the isoelectronic alkaline earth halides, by the resolved fine structure, and, in the case of AlF+, by an ab initio calculation. (3) In the GaCl+, GaBr+, and InBr+ spectra, narrow features accompany the C–X transitions. They are attributed to D 2Σ+–X 2Σ+ transitions, analogous to the alkaline earth halide B 2Σ+–X 2Σ+ band systems. Qualitative electronic state correlations are discussed, and the expected dominant configurations in different regions of the AX+ ground and excited states are given. These are in accord with recent ab initio results on AlF+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455290
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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio calculations on the four lowest electronic states of AlF+ and AlCl+ (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 5133-5141 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The potential energy curves of the two lowest 2Σ+ (X,B) and the two lowest 2Π (A,C) electronic states of the AlF+ and AlCl+ molecular ions have been calculated using highly correlated multireference configuration interaction (MR-CI) wave functions. It is found that both 2Σ+ states and the C 2Πr state are bound, whereas the A 2Πi state is repulsive. Electronic transition moment functions for all six pairs of states of both ions have also been calculated and used for evaluation of the radiative transition probabilities between bound vibrational states. The calculated charge distributions show that the X and C states are dominated by Coulombic attraction between a doubly charged positive aluminum and the singly charged negative halogen ion. The results provide a new assignment of the photoelectron spectra of the neutral AlF. They are also in good agreement with the recently observed optical B–X emission spectra of both molecular ions and C–X bands of AlCl+. The absence of C–X emission of AlF+ is most likely due to predissociation of the C 2Πr state by the repulsive A 2Πi state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461681
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  • 3
    Electronic Resource
    Electronic Resource
    Vibrational-state selective cross sections for the charge transfer H++HCl(X 1∑+)→H(2Sg)+HCl+(A 2∑+,v') (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8962-8969 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational-state selective cross sections have been measured for the endothermic charge-transfer reactions H+,D++HCl(X 1∑+)→H,D(2Sg)+HCl +(A 2∑+,v')−2.67 eV, for collision energies up to 1 keV by means of detecting the spontaneous optical emission of the HCl+(A 2∑+,v'→X 2Πi, v‘) band system. Absolute values between 0.25 and 1 A(ring)2 were obtained by calibration against the known cross section for electron-impact ionization of N2 with subsequent emission of the N+2(B,v'→X,v‘) transition. The charge-transfer cross sections were also calculated using the Landau–Zener theory. The required model parameters were derived from recent ab initio calculations. The energy dependence and the relative magnitude of the cross sections for the product vibrational levels v'=0–5 were closely rendered by the theoretical curves in the velocity range where the Landau–Zener approach applies, i.e., below 200 km/s (≡200 eV for protons). The absolute magnitude of the calculated cross sections also agrees with the measurements within the experimental error limits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461227
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  • 4
    Electronic Resource
    Electronic Resource
    The vacuum ultraviolet photodissociation of silane at 125.1 nm (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 5944-5950 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We observe the photodissociation of SiH4 in a pulsed molecular beam after excitation with 125.1 nm vacuum ultraviolet light generated via resonant four-wave mixing in mercury vapor. Ultraviolet radiation from a Nd:YAG/dye laser combination ionizes the neutral photodissociation fragments and a time-of-flight mass spectrometer detects the ions. The photodissociation signal consists entirely of silicon atoms and silylidyne (SiH) in its first electronically excited state. We see no silylene (SiH2) or silyl radicals (SiH3). Thus, the photodissociation cleaves almost all of the silicon–hydrogen bonds, but the energetics of the dissociation require the production of at least one hydrogen molecule per dissociation event. These results imply that the high energy content of the initially excited Rydberg state prevents formation of the silylene and silyl radicals in stable vibronic states and that dissociation pathways exist that connect the Rydberg state directly to the corresponding silicon atom and silylidyne asymptotes. These pathways are likely to exist because of Jahn–Teller distortion from the initial Td symmetry. Very little of the available energy appears as kinetic energy of the fragments but rather as electronic excitation of the products. Our results differ from those of earlier studies that concluded silylene and silyl are the principle products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465893
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  • 5
    Electronic Resource
    Electronic Resource
    In situ determination of absolute number densities of nitrogen molecule triplet states in an rf-plasma sheath (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 3115-3120 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A laser induced fluorescence technique (LIF) in combination with optical emission spectroscopy (OES) and Rayleigh scattering (RS) was applied to investigate absolute number densities of the population of the three nitrogen triplet states C 3Πu, B 3Πg, and the metastable A 3Σu+ in an asymmetric low pressure rf discharge. Primary targets of this investigation were the three lowest vibrational levels (v=0,1,2) of each triplet state and additionally v=8 of A 3Σu+ which can be populated very efficiently in the plasma sheath. Calibration of LIF intensities to absolute densities of A 3Σu+ and B 3Πg has been realized by comparison with the signal of the RS experiment done in pure nitrogen gas. Calibration of C 3Πu which we could not detect by LIF but rather only by OES was achieved after comparing OES and LIF signals of the B 3Πg state. Excitation energies of the analyzed states range from 6 up to 11.5 eV and the measured number densities differ by about seven orders of magnitude from as much as 1012 cm−3 down to almost 105 cm−3. In addition to the interpretation of the results this article describes the used calibration methods which are partly based on a suggestion made by P. Bogen (Proceedings of the XVI International Conference on Phenomena in Ionized Gases, Invited Papers, edited by W. Bötticher, H. Wenk, and E. Schultz-Gulde, Düsseldorf, 1983, pp. 164–173). © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1351003
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  • 6
    Electronic Resource
    Electronic Resource
    Near-resonant versus nonresonant chemiluminescent charge-transfer reactions of atomic ions with HCl (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1148-1160 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Charge-transfer reactions of C+, O+, F+, Ar+ and some other atomic ions with hydrogen chloride were investigated at collision energies between 〈1 eV and 1 keV. The electronically excited products HCl+ (A 2Σ+) were detected by means of the A 2Σ+→X 2Πi optical emission. In some cases the spectra showed, at low collision energies, an enhanced excitation of specific vibrational HCl+(A,v') levels: for C+, v'=1; for O+, v'=3 as well as v'=1; and for F+, v'=6. These levels are populated in near-resonant, slightly exothermic processes. Their rotational temperature was on the order of 600–700 K. For the other vibrational levels the excitation is off-resonance, mostly endothermic, and here the rotational temperature was 1000–4000 K. Corresponding data are also given for DCl. The selectivity for certain vibrational states is explained by crossings between the vibronic entrance and exit state energy surfaces, calculated from classical electrostatic multipole potentials. The cross sections for the near-resonant reactions decrease monotonically with increasing collision energy, while for the endothermic channels they rise steeply from threshold to a plateau. With argon ions the excitation function exhibits an unusual shape. Here the charge-transfer cross sections for all vibrational levels go through a maximum just above threshold, which is followed by a distinct minimum at about 10 eVc.m.. This may be due to formation of a long-lived collision complex (Ar–HCl)+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466645
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  • 7
    Electronic Resource
    Electronic Resource
    Measurement of the HCl+(A 2Σ+–X 2Π) electronic transition moment using quasiresonant charge transfer at low energy (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3475-3480 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: HCl+(A) was selectively prepared in the v'=0, 3, 5, and 6 levels using ion impact excitation. The resulting A–X spectra are largely free from band overlap. From intensity measurements on 16 bands, the electronic transition moment function M(R) was derived in the region of R=1.1–1.8 A(ring). Computer simulations based on this M(R) function were performed both for these and for additional spectra excited by electron impact. In all cases an excellent reproduction of the measured spectra was achieved. The M(R) dependence obtained in this work agrees very well with a large-scale ab initio calculation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453896
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