“…The population is calculated from the same sequence (Δ v = −1) where the peaks for analysis are well resolved. The population is obtained from the band-head intensities divided by the Franck−Condon factors and the frequency factor of ν 3 . The calculated population also agrees with the results from other sequences (Δ v = 0 and −2) where fewer peaks were resolved.…”
The ionic and luminous photofragments of allene excited with a single focused laser beam at 193 nm are detected using time-of-flight mass spectrometry and dispersed emission spectroscopy, respectively. The major ionic products detected are C 3 + , C 2 + , and C + . The yields of C 3 H n + (n ) 1-3) are minor compared to the carbon ions. For the emission spectra, the C 2 Swan system (, and an atomic line corresponding to the C(2p3s 1 P o ) f C(2p 2 1 S) transition are the major features observed. The vibrational population in the C 2 (d 3 Π g ) state is found inverted to a thermal equilibrium distribution. The laser-power dependence of each photofragment is measured, from which multiphoton dissociation and ionization mechanisms of allene are proposed. A kinetic model is developed to further illuminate the photodissociation mechanisms. Although C n + (n ) 1-3) ions are the major species observed in the present photodissociation experiment, C 3 H n + (n ) 1-4) are most abundant in the electron impact of allene. The hydrogen elimination and carbon-carbon bond rupture in the photodissociation of allene at 193 nm, with C n and C 3 H n (n ) 1-3) photofragments, are concluded to precede the competing multiphoton ionization process, in producing C 3 H 4 + , within the laser flux (<2.7 × 10 26 photons cm -2 s -1 ) used in this experiment.
“…The population is calculated from the same sequence (Δ v = −1) where the peaks for analysis are well resolved. The population is obtained from the band-head intensities divided by the Franck−Condon factors and the frequency factor of ν 3 . The calculated population also agrees with the results from other sequences (Δ v = 0 and −2) where fewer peaks were resolved.…”
The ionic and luminous photofragments of allene excited with a single focused laser beam at 193 nm are detected using time-of-flight mass spectrometry and dispersed emission spectroscopy, respectively. The major ionic products detected are C 3 + , C 2 + , and C + . The yields of C 3 H n + (n ) 1-3) are minor compared to the carbon ions. For the emission spectra, the C 2 Swan system (, and an atomic line corresponding to the C(2p3s 1 P o ) f C(2p 2 1 S) transition are the major features observed. The vibrational population in the C 2 (d 3 Π g ) state is found inverted to a thermal equilibrium distribution. The laser-power dependence of each photofragment is measured, from which multiphoton dissociation and ionization mechanisms of allene are proposed. A kinetic model is developed to further illuminate the photodissociation mechanisms. Although C n + (n ) 1-3) ions are the major species observed in the present photodissociation experiment, C 3 H n + (n ) 1-4) are most abundant in the electron impact of allene. The hydrogen elimination and carbon-carbon bond rupture in the photodissociation of allene at 193 nm, with C n and C 3 H n (n ) 1-3) photofragments, are concluded to precede the competing multiphoton ionization process, in producing C 3 H 4 + , within the laser flux (<2.7 × 10 26 photons cm -2 s -1 ) used in this experiment.
“…We have therefore calculated a new grid of model atmospheres, which takes into account the blanketing effect of 537 bands from the Swan, Deslandresd'Azambuja, Fox-Herzberg, Phillips, and Ballik-Ramsay systems, as well as numerous atomic carbon lines and the resonance lines of HeI in the EUV. The general molecular data were taken from Huber & Herzberg (1979), the Franck-Condon factors for the vibrational transitions from various sources (Krishnaswamy & Odell 1977;Dwivedi et al 1978;Spindler 1965;Sharp 1983). Molecular absorption is treated with the "just overlapping line approximation (JOLA)" in the version as described in Zeidler-K.T.…”
Section: Model Atmosphere Analysis Of Gsc2u J1311472+292348mentioning
Abstract.A new model atmosphere analysis for the peculiar DQ white dwarf discovered by Carollo et al. (2002) is presented. The effective temperature and carbon abundance have been estimated by fitting both the photometric data (UB J VR F I N JHK) and a low resolution spectrum (3500 < λ < 7500 Å) with a new model grid for helium-rich white dwarfs with traces of carbon (DQ stars). We estimate T eff 5120 ± 200 K and log[C/He] −5.8 ± 0.5, which make GSC2U J131147.2+292348 the coolest DQ star ever observed. This result indicates that the hypothetical transition from C 2 to C 2 H molecules around T eff = 6000 K, which was inferred to explain the absence of DQ stars at lower temperatures, needs to be reconsidered.
“…The assignment of this spectrum, referred to in the text as the chemiluminescence spectrum of GAP, is discussed in section 4. The positions and relative intensities of the calculated spectra were taken from the following sources: CN, , CH, C 2 , NH, OH 4 Chemiluminescence intensity of CN* (measured at 387 nm) as a function of pressure and laser fluence.…”
Previous studies of GAP (glycidyl azido polymer) laser-induced decomposition (Propellants, Explosives,
Pyrotechnics
1996, 21, 258), revealed that the shock wave produced from a diluted polymer is more energetic
than from the neat polymer. In this paper, direct measurement of the energy disposal into molecular products
is reported using spectroscopic methods. Chemiluminescence probes electronically excited species, and laser-induced fluorescence, ground-state radicals. It is found that the initial velocity and internal energy content of
small diatomic molecules is larger in some diluted polymers than in the neat one. This finding is in line with
a simple model based on the assumption of a self-sustained reaction following initial laser excitation.
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