Detection of the silylene ν2 band by infrared diode laser kinetic spectroscopy

Abstract

The ν2 band of the silylene SiH2 molecule in X̃ 1 A1 was observed for the first time in the gas phase by using infrared diode laser kinetic spectroscopy. Silylene molecules were generated by the photolysis of phenylsilane at 193 nm. The observed spectrum was analyzed to determine the rotational and centrifugal distortion constants in the ground and v2 =1 states and the band origin ν0 =998.6241(3) cm−1 with one standard deviation in parentheses. The significance of the derived parameters is discussed in detail.

Absorption spectroscopy of SiH2 near 640 nm

“…We have also determined the equilibrium r e structure of silylene in this singlet excited state. The accuracy of the line positions is about 0.01 cm Ϫ1 , which is intermediate between the high resolution infrared experiment of Yamada et al 10 and the previous data from Dubois. 7,8 We also present a more comprehensive determination of the rotational constants of the ͑0,0,0͒ level in the electronic ground state, performed by combining all three sets of data with appropriate weights in a single refinement process.…”

“…To these we added our data from this work, and those of Yamada et al 10 on the 2 fundamental. Considering the different accuracy of each data set, we gave relative weights of 0.1, 1 and 10 to individual transitions belonging to each set, respectively.…”

“…A detectivity of the order of 10 8 SiH 2 /cm 3 was achieved. 22 First Dubois, 8 and later Yamada et al, 10 determined the ground state rotational constants of SiH 2 , and hence the r 0 structure, by making ground state combination differences from their respective data. Based on the similar structure of SiH 2 and SH 2 , Yamada et al extended their calculation to derive the equilibrium geometrical structure of silylene by means of the rovibrational constants ␣ i B of the SH 2 molecule, which had been reported before.…”

“…The strong rotational perturbations in the à 1 B 1 state have been related 4 to the unusual radiative lifetimes recently measured by laser-induced fluorescence ͑LIF͒ by Thoman, Steinfeld and coworkers. 5,6 In the 1 A 1 state, Yamada et al 10 studied the 2 band by means of an infrared diode laser spectrometer, thus providing the only high resolution infrared data available for this radical up to this moment. Several authors have reported the LIF detection of silylene produced by multiphoton or UV dissociation of silane compounds.…”

“…Based on the similar structure of SiH 2 and SH 2 , Yamada et al extended their calculation to derive the equilibrium geometrical structure of silylene by means of the rovibrational constants ␣ i B of the SH 2 molecule, which had been reported before. 10 Allen and Schaefer 25 have performed the most comprehensive theoretical calculation on the geometrical structure, force constants and vibrational spectra of SiH 2 ͑as well as SiH, SiH 3 and SiH 4 ) for all three electronic states mentioned above. They report also the estimated rovibrational constants ␣ i B for each state.…”