The distortion moment spectrum of GeH4: the microwave Q branch

Ten pure rotational Q-branch transitions of the distortion moment spectrum of GeH4 have been measured between 9 and 23 GHz. They were observed in a conventional Stark modulated spectrometer modified to have a sensitivity of 1 × 10−11 cm−1. No Ge isotope splitting was observed in the spectrum. The spectrum was analysed in terms of a single set of six tensor centrifugal distortion constants DT, H4T, H6T, L4T, L6T, and L8T. The results were found to predict accurately transitions previously reported from infrared–microwave double resonance spectroscopy, and a complete analysis using both sets of data was carried out. The results are (in hertz): DT = 67 775.54 ± 0.86; H4T = −5.3827 ± 0.0055; H6T = 2.9693 ± 0.0019; L4T = (3.996 ± 0.088) × 10−4; L6T = −(4.122 ± 0.050) × 10−4; L8T = −(8.01 ± 0.14) × 10−4. The errors here are the standard deviations obtained from the least-squares analysis; estimates of the absolute errors are also given. For possible application in other high resolution studies, the constants have been used to calculate all tensor splittings for J ≤ 20.