MEASUREMENT OF THE 1ST EXCITED BENDING STATE OF AR-CO USING A NEW CONCENTRATION MODULATION TECHNIQUE IN THE JET

Using a new modulation scheme: concentration-frequency double modulati on, we were able to observe a new band of Ar CO in the infrared. We as signed 20 lines of the transition from the ground state, K = 0, to the combination band of upsilon(CO) = 1 and first excited bending, K = 0 state of Ar-CO. The lower state is identical to the state found by McK ellar et al., who measured the perpendicular transitions in the CO fun damental branch of Ar CO. The band origin of this K: 0 --> 0 transitio n is situated at 2154.7460 cm-1. The K = 0 first excited bending state of Ar-CO is found to be 11.9 cm-1 higher in energy than the K = 0 gro und state. This is the first experiment, which determines the bending energy of the Ar-CO complex. Theoretical predictions were made by Tenn yson et al. and Parish et al. They predicted this state to be located at 14.1 cm-1 and 13 cm-1 respectively, whereas experimentally we found a value of 11.914 cm-1. We will present spectroscopic results and det ails on the new modulation scheme. This technique uses concentration m odulation in a c.w. supersonic jet expansion by an a.c. discharge and allows high repetition rates (kHz) in combination with a high duty cyc le (50%).