Rotational spectra of indole in the lowest vibrational states

Abstract The millimetre- and submillimetre-wave rotational spectra of indole (C8H7N) have been recorded in several frequency regions from 140 to 715 GHz. Nearly 6,000 rotational transitions corresponding to the ground and two vibrational excited states ν42 and ν41 were assigned and analysed using the A-reduced Hamiltonian. All newly measured transitions were fitted together with the previously published data yielding significantly improved rotational and centrifugal distortion constants. Such highly precise molecular parameters could support future searches of the spectral features of indole in the interstellar medium as this molecule is the simplest prototype of polycyclic N-substituted aromatic hydrocarbons (PANHs), the possible sources of unidentified infrared emission in the interstellar medium.