Orbital angular momentum (Renner–Teller) effects in the Πi2 ground state of silicon methylidyne (SiCH)

Abstract

The ground state vibrational energy levels of jet-cooled SiCH and SiCD have been studied by a combination of laser-induced fluorescence and wavelength-resolved fluorescence techniques. The radicals were produced by a pulsed electric discharge at the exit of a supersonic expansion using tetramethylsilane or methyltrichlorosilane as the precursor. Emission spectra have been obtained by pumping both perpendicular and parallel (vibronically induced) bands, providing complementary information on the Si–C stretching and Si–C–H bending modes. Ground state energy levels up to 4000 cm−1 have been assigned and fitted using a vibrational Hamiltonian that incorporates Renner–Teller, spin–orbit, vibrational anharmonicity, and Fermi resonance interactions. The validity of the derived parameters has been tested using the isotope relations.

Near-infrared diode laser spectroscopy of the HCSi radical

“…The present value (495.00698(30) cm À1 ) is rather close to a value of 490.26 cm À1 obtained for a quantity expressed as x 2 ð¼ 508:03 cm À1 Þ þ 4g 4 À g K , which is shown in Smith et al [4] to correspond approximately to the origin of theX 2 P i ð0 1 0Þ state.…”

“…As seen in Table 1, the Renner-Teller parameter e obtained in the present study is little bit larger than that determined by Smith et al [4]. The value of the parameter e determined from theX 2 P i ð0 1 0Þ state analysis depends completely on the value of the vibrational frequency x 2 , for which the value of origin of thẽ X 2 P i ð0 1 0Þ state was used in the present analysis.…”

“…The value of 495.00698(30) cm À1 for the origin of thẽ X 2 P i ð0 1 0Þ state obtained in the present study should not be compared with a value of 508.03(38) cm À1 determined for the vibrational frequency x 2 by Smith et al [4] (27) )0.000055 (13) )0.00014(1) c 0.00045 (31) This work Smith et al [4] (…”

“…The least squares fit with 20 adjustable constants and equal weights for all the energy differences resulted in a standard deviation of 0.0040 cm À1 , which is almost comparable to the experimental uncertainty expected for such combination differences. The molecular constants thus determined are shown in Table 1, where those obtained in previous investigations by other researchers [1][2][3][4] are given for comparison. It is seen that the constants for theX 2 P i ð0 0 0Þ state in the present study are rather close to those obtained from the analysis of the emission spectrum by Cireasa et al [1,3], where a spin-rotation interaction constant c was used (the constant c was undetermined in the present fit).…”

“…On the other hand, the HCSi radical is a very fascinating molecular species from the spectroscopic viewpoint because it shows a Renner-Teller effect in the ground electronic state. Recently, several spectroscopic investigations [1][2][3][4][5][6] were published, including studies on rotationally resolved spectra associated with the groundX 2 Pð0 0 0Þ state and theà 2 R þ excited states [1][2][3], a study of the vibrational energies related to the Renner-Teller effect in theX 2 P state [4], a study of the hyperfine structure and Stark effect in theX 2 P andà 2 R þ states [5], and an ab initio study characterizing the Renner-Teller effect [6]. The present investigation was carried out to obtain detailed information on the Renner-Teller interaction by studying the rotational energy levels in theX 2 Pð0 1 0Þ state, which have not been previously investigated.…”