Infrared – Radio-frequency Double Resonance Observations of Δ <i>J</i> = 0 ‘Forbidden’ Rotational Transitions of SiH₄

Abstract

The radio-frequency and microwave spectrum of SiH 4 corresponding to ΔJ = 0 ‘forbidden’ rotational transitions between the centrifugal distortion multiplets of levels has been studied by using the method of infrared–microwave double resonance in a laser cavity. Coincidences between the v 4 fundamental band of SiH 4 and N 2 O infrared laser lines in the 10 μm region have been used. Seven double resonance signals have been found and four of them were assigned to the J = 5, and J = 9 'forbidden' rotational transitions. From the measured frequencies, the quartic and sextic centrifugal distortion constants were determined as D 1 = 74 861 ± 15 Hz, H 4t = −7.14 ± 0.3 Hz, and H 6t = 6.57 ± 1.1 Hz.