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

Abstract

The microwave spectrum of 2-iodopropene has been investigated between 7.7 and 18 GHz. The measured transition frequencies of the ground and two vibrationally excited states have been analyzed using direct diagonalization of the rotational and quadrupole Hamiltonian. The following rotational and quadrupole coupling constants have been determined in a leastsquares fit for the ground state: A = 9285.153(20) MHz; B = 2337.2198(14) MHz; C = 1887.5871(14) MHz; and χ cc = −1820.783(33) MHz; χ ab = 147.5(10) MHz; χ bb = 957.018(41) MHz; and χ cc = 863.765(40) MHz. The quadrupole coupling constants have been transformed to their principal axis system. From the splittings of some transitions of the first torsionally excited state a value of V 3 = 905(3) cm −1 has been found for the threefold barrier hindering the internal rotation of the methyl group.