The Forbidden Pure Rotational Spectrum of SiH4: the R Branch

Abstract

The R branch of the pure rotational spectrum of SiH4 in the ground vibronic state has been studied in the spectral region 60 to 134 cm−1 using a Michelson interferometer and a 10.6 m cell. Thirteen lines have been observed and identified as forbidden (J → J + 1) transitions for rotational levels from 10 to 22, with the absorption mechanism being provided by the centrifugal distortion dipole moment μD. The two strongest competing mechanisms are discussed and eliminated from consideration: transitions within the vibrational excited state ν4 and the difference band ν2 – ν4. In the data analysis, the frequency shift due to the fourth rank tensor distortion interaction is taken into account by an extension of the earlier work on GeH4 by Ozier and Rosenberg. It has been determined that the rotational constant B0 = (2.8574 ± 0.0027) cm−1 and the scalar distortion constant Ds = (3.48 ± 0.54) × 10−5 cm−1. From estimates of the line intensities, it has been found that [Formula: see text].