Infrared, diode laser spectroscopy of the Ar–N2O complex: Observation of the intermolecular bending mode in combination with the highest frequency intramolecular stretching mode

Rotationally resolved vibrational spectra consisting of a-type transitions have been observed for the low-frequency, intermolecular bending mode in combination with the highest frequency, intramolecular stretching mode of Ar–N2O. Analysis of the spectral data places the origin of the combination band at 2256.1 cm −1 while the origin of the intramolecular stretching fundamental is at 2223.9 cm−1. The difference between these two origins is approximately 32.2 cm−1 and agrees well with our calculated frequency of 31.5 cm−1 for the intermolecular bending mode, which was obtained by analysis of the centrifugal distortion constants. In addition, argon–nitrous oxide exhibits an anomalously large inertial defect of 10.96 amu Å2 in the combination state. This indicates a breakdown in the assumption of separation between vibration and rotation. While much of the inertial defect in the ground state can be accounted for by including Coriolis interactions, that occurring in the combination state is only partially accounted for by a similar analysis. Small, but significant changes, are observed in both the radial and angular parameters for Ar–N2O when going from the ground to the combination state, indicating large amplitude motion. The combination band is approximately 200 times less intense than the high-frequency, stretching fundamental of Ar–N2O. In addition, over 400 new rovibrational transitions are assigned to the previously observed 101 intramolecular stretching fundamental of the complex, and the subsequent rotational analysis is found to be in close agreement with earlier studies. Data were taken on a newly built, rapid-scan, diode laser spectrometer that incorporates a 12 cm×200 μm pulsed slit-expansion nozzle.