VARIATION OF BR QUADRUPOLE COUPLING WITH ISOTOPIC SUBSTITUTION IN METHYL-BROMIDE

The J = 0 ← 1 transitions in CH379Br (I), CH381Br (II), CD379Br (III), and CD381Br (IV) were measured using a Stark-cell spectrometer constructed from C-band waveguide. High-resolution spectra yielded precise values for the bromine quadrupole coupling strength. Values obtained were eqQ(I) = -577.08 ± 0.15 MHz, eqQ(II) = -482.18 ± 0.15 MHz, eqQ(III) = -575.66 ± 0.15 MHz, and eqQ(IV) = -480.89 ± 0.15 MHz. The observed center frequencies for the J = 0 ← 1 transitions are ν0(I) = 19136.35 ± 0.03 MHz, ν0(II) = 19063.62 ± 0.03 MHz, ν0(III) = 15429.23 ± 0.03 MHz, and ν0(IV) = 15362.41 ± 0.03 MHz. A 0.26 ± 0.02% decrease in bromine quadrupole coupling is observed when the methyl group is fully deuterated. This is in agreement with, and supports interpretations given for, previous results on methyl chloride. © 1979.