The vibrational spectrum and molecular constants of silicon dihydride SiH2in the ground electronic state

The infrared spectrum of SiH2 was observed in the 5 mu m region by using di ode laser spectroscopy, and the three bands v(1), 2v(2), and v(3) were reco rded and assigned. A separate analysis of the three bands yielded the band origins, 1995.9280, 1987.6938, and 1992.816 cm(-1), respectively, thereby e stablishing that v(1) is higher than 2v(2), contrary to the result of a pre vious matrix study. The anharmonic resonances, both v(1)/2v(2) Fermi and 2v (1)/2v(3) Darling-Dennison, which were observed in the laser induced fluore scence spectra previously reported, were reanalyzed by removing the conditi on v(1)<2v(2), leading to a much improved set of vibrational parameters. Th e harmonic frequencies of SiH2 were then obtained to be omega(1) = 2076.55, omega(2) = 1020.49, and omega(3) = 2065.65 cm(-1). Molecular constants of SiH2 in the ground vibronic state were reexamined in light of the present a s well as other spectroscopic results recently obtained on the molecule. (C ) 1999 American Institute of Physics. [S0021-9606(99)30109-4].