Measurement of the first excited bending state of Ar-CO using a new concentration modulation technique in the jet

Abstract

Using a new modulation scheme: concentration-frequency double modulation, we were able to observe a new band of Ar-CO in the infrared. We assigned 20 lines of the transition from the ground state, K = 0, to the combination band of ν_CO = 1 and first excited bending, K = 0 state of Ar-CO. The lower state is identical to the state found by McKellar et al., who measured the perpendicular transitions in the CO fundamental branch of Ar-CO. The band origin of this K : 0 → 0 transition is situated at 2154·7460 cm^-1. The K = 0 first excited bending state of Ar-CO is found to be 11·9cm^-1 higher in energy than the K = 0 ground state. This is the first experiment, which determines the bending energy of the Ar-CO complex. Theoretical predictions were made by Tennyson et al. and Parish et al. They predicted this state to be located at 14·1cm^-1 and 13cm^-1, respectively, whereas experimentally we found a value of 11·914cm^-1. We will present spectroscopic results and details on the new modulation scheme. This technique uses concentration modulation in a c.w. supersonic jet expansion by an a.c. discharge and allows high repetition rates (kHz) in combination with a high duty cycle (50%).