Rotationally resolved overtone spectroscopy of the NO–Ar complex

The infrared absorption spectrum of the NO–Ar complex is measured in the region of the first NO overtone band using a new type of IR–UV double resonance technique which combines IR excitation with (2+1) resonance enhanced multiphoton ionization detection. The long lifetime of the complex (⩾30 ns) allows the sensitive detection of the vibrationally excited complex itself. Two bands corresponding to ΔP=0 and ΔP=+1 transitions are observed at 3723.4 and 3727.4 cm−1. The rotational analysis is based on a rigid rotor model Hamiltonian and yields the rotational constants A′=1.795(5) cm−1, B′=0.0785(2) cm−1, and C′=0.0615(1) cm−1. The observed splitting of rotational lines is consistent with an increased quenching constant ζ′=4.0(5) cm−1.