Cyanonaphthalenes (C10H7CN) are bicyclic, nitrogen-substituted polycyclic aromatic hydrocarbons and the first polycyclic species detected in the interstellar medium via radioastronomy. Here, we report a combined experimental and computational study of 1- and 2-cyanonaphthalene, extending and improving the spectroscopic characterization of their rotational and vibrational spectra. Gas-phase far-infrared vibrational spectra were measured in the 50–650 cm–1 region with a Fourier-transform infrared spectrometer, providing the first gas-phase experimental vibrational band centers for these molecules. Pure rotational spectra were recorded between 75 and 220 GHz using chirped-pulse Fourier-transform and source-frequency-modulation spectroscopy, enabling extended observation of transitions in the ground vibrational states as well as the first spectroscopic characterization of low-lying vibrational states of energies lower than 200 cm–1. While density functional theory calculations guided initial spectral assignments, high-level coupled cluster computations were also performed and compared with experiment, yielding highly accurate fundamental vibrational frequencies and rotational constants for both ground and excited vibrational states.
Bentley et al. (Mon,) studied this question.