Eur. Phys. J. D (2016) 70: 259
https://doi.org/10.1140/epjd/e2016-70569-6

Regular Article

Infrared activation due to dynamic symmetry-breakdown in polyatomic molecules

Department of Physics, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, 171-8588 Tokyo, Japan

^a e-mail: koichiro.yamakawa@gakushuin.ac.jp

Received: 8 September 2016
Received in final form: 22 October 2016
Published online: 6 December 2016

Abstract

Polyatomic molecules undergo symmetry breakdown upon vibration in contrast to diatomic ones and therefore have some infrared-inactive vibrational modes which are excited through the dipole transition owing to coupling with other modes. It is both the anharmonic potentials and high-order derivatives of the dipole operator with respect to the normal coordinates that cause the fundamental bands of inactive modes. Individual molecules with specific symmetries are discussed in detail, so that the modes which are activated by the dynamic symmetry-breakdown become clear.