Microwave spectrum, quadrupole coupling constants, and barrier to internal rotation of 2-bromopropene

Abstract

The microwave spectra of CH 2C 79BrCH 3 and CH 2C 81BrCH 3 have been investigated in the frequency region from 8–12 Gc/sec. Particular consideration has been given to the quadrupole interaction which was treated through the exact diagonalization of the rotational and quadrupole energy matrix. The following rotational constants and quadrupole coupling constants in the vibrational ground state have been found for CH 2C 79BrCH 3: A = 9255.1 ± 5.3 Mc/sec, B = 3137.99 ± 0.03 Mc/sec, C = 2375.89 ± 0.04 Mc/sec, χ aa = 534.5 ± 6.1 Mc/sec, χ bb = −286.5 ± 4.8 Mc/sec, χ cc = −248.0 ± 4.1 Mc/sec, and χ ab = 60 ± 10 Mc/sec; for CH 2C 81BrCH 3: A = 9254.6 ± 5.3 Mc/sec, B = 3112.88 ± 0.04 Mc/sec, C = 2361.42 ± 0.06 Mc/sec, χ aa = 446.6 ± 3.5 Mc/sec, χ bb = −239.0 ± 2.5 Mc/sec, χ cc = −207.6 ± 3.3 Mc/sec, and χ ab = 60 ± 10 Mc/sec. The splittings of several Q-branch transitions of the first excited torsional state due to the internal rotation of the methyl group have been analyzed yielding a value of 2695 ± 30 cal/mole for the barrier. A comparison is given for the barrier heights determined for different series of halogen compounds.