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

Abstract

The radio-frequency and microwave spectrum of SiH4 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 v4 fundamental band of SiH4 and N2O 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 D1 = 74 861 ± 15 Hz, H4t = −7.14 ± 0.3 Hz, and H6t = 6.57 ± 1.1 Hz.