The distortion moment spectrum of 28SiH4: The microwave Q branch

Abstract

Eleven pure rotational Q-branch transitions have been observed between 8 and 25 GHz in the distortion moment spectrum of 28SiH4. The spectrometer used was a conventional Stark-modulated instrument modified to have a sensitivity of ~1 × 10−11 cm−1. From the eleven frequencies, values have been determined for the single quartic tensor distortion constant DT, the two sextic constants H4T and H6T, and the three octic constants L4T, H6T, and L8T. These are (in Hz): DT = (74 751.4 ± 1.6); H4T = −(6.044 ± 0.010); H6T = (2.598 ± 0.003); L4T = (46.5 ± 1.5) × 10−5; L6T = −(37.9 ± 0.8) × 10−5; L8T = −(76.6 ± 2.1) × 10−5. The errors here are the standard deviations obtained from a least squares analysis; estimates are also given of the absolute errors. For possible application in other high resolution studies of silane, the constants have been used to calculate all Q-branch splittings for J ≤ 20. The present results are compared to those obtained by double resonance methods by Kreiner and Oka; a definite identification has been found for one of their lines which had previously been tentatively assigned to another transition. The combination-differences data of Pierre, Guelachvili, and Amiot have been reanalysed on the basis of the current results to obtain improved values of the rotational constant and the quartic and sextic scalar distortion constants.