The rotational spectrum of acrylonitrile in excited states of the two low-frequency CCN bending vibrational modes

Abstract

The strongest vibrational satellites in the rotational spectrum of acrylonitrile have been assigned and frequencies of μ a - and μ b -type transitions in the frequency range 27–184 GHz are reported for the first two excited states in the lowest frequency in-plane CCN bending vibrational mode and the first excited state in the out-of-plane CCN bending mode. The values of the rotational constants, the quartic and sextic centrifugal distortion constants, and one octic centrifugal distortion constant are determined for each of these states. Less extensive results are also presented for the third quantum of the in-plane bend. The data set for the ground state has been extended by a number of new measurements and the improved ground state constants are used in a discussion of changes in rotational and centrifugal distortion constants with vibrational state where all constants associated with P z n and P 2 P z ( n−2) terms in the Hamiltonian are found to reflect the common origin of the two CCN bends.