Knowledge Bank

The fluorescence excitation spectrum of the Ar-HCO van der Waals complex in the vicinity of the $B~2A\prime (000)-X~2A\prime (000)$ band of free HCO is reported. At least 8 bands associated with the complex have been detected. We observe a spectral shift of the lowest energy Ar-HCO band with respect to the origin of the free HCO transition, and from this estimate the binding energy in the excited electronic state to be at least $10cm-1$ greater than that in the ground state. Rotational analysis of some of the bands has been carried out, and average Ar-HCO separations in both electronic states determined. Several of the bands were assigned as hot bands from the first excited bend-stretch level $(K\prime \prime =1)$ in the ground electronic state. Decay lifetimes of several Ar-HCO $(B~)$ levels were found to be somewhat smaller than those previously measured for free HCO.