Gas-phase infrared spectroscopy on the lowest triplet state of the pyrazine–argon complex

The infrared (IR) absorption spectrum of the jet-cooled pyrazine–argon Van der Waals complex in its lowest triplet state is measured. Vibrational excitation of the laser-prepared triplet state by IR absorption causes dissociation of the complex, which is monitored via the depletion of the pyrazine–argon ion signal. A total of 10 vibrational transitions are detected in the 500–1500 cm−1 region. Comparison of these data with ab initio calculations might help to elucidate the nature of the distortion of the lowest triplet state by other electronically excited states.