Aromatic and Acetylenic C–H or C–D Stretching Bands Anharmonicity Detection of Phenylacetylene by UV Laser-Induced Vibrational Emission

The anharmonic infrared (IR) emission spectra of phenylacetylene C 6 H 5 CCH and an isotopologue C 6 H 5 CCD induced by 193 nm UV excitation have been investigated in the gas phase. The study has been operated with a homemade IR spectrometer enabling to record time- and wavelength-resolved spectra between 2.5 and 4.5 μm, emitted all along the collisional cooling. The analysis is supported by a kinetic Monte Carlo simulation in the vibrational harmonic approximation. For both species, the anharmonic shifts of the acetylenic C–H or C–D stretching modes and the aromatic C–H stretching modes are studied for band positions and bandwidths in terms of the internal energy. For C 6 H 5 CCD, the internal energy dependence of the emission intensity band ratio is investigated and rationalized. This work demonstrates the potential of time-resolved IR emission spectroscopy to explore anharmonicity of astrophysically relevant molecules.