Millimeter Wave Spectra and Centrifugal Stretching Constants of the Methyl Halides

Abstract

High J transitions of the methyl halides have been measured and have been used to calculate accurate values for the centrifugal distortion constants. The values obtained for BO, DJJ, and DJK are (in Mc/sec and kc/sec, respectively); CH3·F19, 25 536.11, 59.3, 445; CH3·Cl35, 13 292.86, 18.1, 198; CH3·Br79, 9568.20, 9.9, 128.3; CH3·Br81, 9531.82, 9.7, 127.4; CH3·I127, 7501.30, 6.28, 98.5. The new DJJ value for CH3·Cl35 is in good agreement with the value of 18.4 kc/sec theoretically predicted by Chang and Dennison. For all four molecules the DJJ constants were found to be in good agreement with those predicted from Kratzer's formula D JJ =4B O 3 /ω 2 , where ω is the vibrational frequency corresponding to the stretching of the carbon halogen bond.