Single vibronic level emission spectroscopy of jet-cooled HSiF and DSiF

Abstract

Using the technique of single vibronic level emission spectroscopy, the ground state vibrational manifolds of jet-cooled HSiF and DSiF have been studied. The radicals were produced in a pulsed electric discharge jet using trifluorosilane (HSiF3 or DSiF3) as the precursor. The gas phase ground state harmonic vibrational frequencies of both isotopomers have been determined for the first time. A normal coordinate analysis using the vibrational frequencies and literature values for the centrifugal distortion constants allowed the determination of all six ground state force constants. Our previous ground state rotational constants have been combined with the calculated harmonic contributions to the α constants to obtain an average (rz) structure and an estimate of the equilibrium (rez) structure. The reliability of the force constants has been evaluated by Franck–Condon simulations of the emission spectra and comparisons of the calculated and experimentally determined inertial defects.

Franck–Condon simulation of the single vibronic level emission spectra of HSiF and DSiF including anharmonicity

“…First, the extent of mixing of the vibrational states within a combination manifold, as shown in the calculated anharmonic wave functions, is dependent on the closeness of the calculated energies of the vibrational levels within the manifold, which is dependent on the level of theory used to obtain the PEF of the X 1 AЈ state. The difference between the computed fundamental frequencies of the bending and SiF stretching modes of 15 cm Ϫ1 is in reasonably good agreement with the corresponding experimental difference of 21 cm Ϫ1 reported in HCJ01 1 ͑see Table IV and later text͒, suggesting that the PEF of the X 1 AЈ state should be reasonably reliable. In this connection, the calculated anharmonic wave functions reported here should give a reasonably accurate description of the mixing.…”

“…The top spectrum labeled ͑a͒ in each figure is the observed spectrum from HCJ01. 1 In all figures, the simulated spectra labeled ͑b͒, ͑c͒, and ͑d͒, below ͑a͒, have the following geometrical parameters of the à 1 AЉ state ͓in all simulated spectra, the X 1 AЈ state has its geometrical parameters fixed to r e (SiF) ϭ1.603 Å, r e (HSi)ϭ1.529 Å, and e (HSiF)ϭ96.6°, the estimated r e z values from HCJ01; 1 see Table 3͔: ͑b͒ r e (SiF)ϭ1.597 Å, r e (HSi)ϭ1.526 Å, and e (HSiF) ϭ116.0°͑the IFCA geometry with the best overall match; see later text͒; ͑c͒ r e (SiF)ϭ1.597 Å, r e (HSi)ϭ1.526 Å, and e (HSiF) ϭ115.0°͑experimentally derived r e geometrical parameters from Ref. 3͒; and ͑d͒ r e (SiF)ϭ1.6097 Å, r e (HSi)ϭ1.5226 Å, and e (HSiF) ϭ116.9°͑ab initio geometry change͒.…”

“…In addition, 2 Љ and 3 Љ may not correspond to the bending and SiF stretching mode, respectively, as conventionally assumed ͑e.g., in HCJ01͒. 1 Nevertheless, for the sake of simplicity and ease of comparison with the vibrational assignments given in HCJ01, 1 we will still use the vibrational labels obtained in the way mentioned above and will not make a distinction between the vibrational designations used here and in HCJ01. It should be borne in mind that, for higher energy vibrational levels of the X 1 AЈ state of HSiF, 2 Љ and 3 Љ may not be good quantum numbers and may not correspond to the bending and SiF stretching modes, respectively, as assumed in HCJ01, because of strong coupling.…”

“…1 The relative intensity of each vibrational component in a simulated spectrum is given by the corresponding computed anharmonic FC factor and a frequency factor of power 4.…”

Ab initio calculations on SnCl2 and Franck-Condon factor simulations of its ã-X̃ and B̃-X̃ absorption and single-vibronic-level emission spectra

“…9,12 Nevertheless, several other spectroscopic techniques, including laser induced fluorescence ͑LIF͒ spectroscopy [16][17][18][19] and ultraviolet absorption spectroscopy, [20][21][22][23] have been used routinely to measure the densities of reactive intermediates in processing-type plasmas, such as in flame, laser, hot filament, and plasma enhanced CVD processes in the semiconductor industry. [24][25][26][27][28][29] Prior to in situ monitoring of gaseous species in a CVD reactor, the spectroscopic technique of LIF followed by dispersed fluorescence ͓single-vibronic-level ͑SVL͒ emission͔ has been employed extensively in the laboratory to characterize the reactive gas-phase species [30][31][32][33][34][35][36][37] to be monitored in the CVD process. In this connection, we propose in the present study to carry out a combined ab initio/Franck-Condon factor investigation on the absorption and SVL emission spectra of SnCl 2 , yet to be recorded.…”