Fluorescence excitation spectroscopy of the Ar-HCO((X)over-tilde(2)A',(B)over-tilde(2)A') van der Waals complex

The fluorescence excitation spectrum of the Ar-HCO van der Waals complex in the vicinity of the (B) over tilde(2)A'-(X) over tilde(1)A' 0(0)(0) band of free HCO is reported. At least eight bands associated with the complex have been detected. From the spectral shift of the lowest energy Ar-HCO band from the origin of the free HCO transition, we estimate the Ar-HCO binding energy in the excited electronic state to be at least 13 cm(-1) greater than that in the ground state. Rotational analysis of some of the bands has been carried out, and average Ar-HCO separations (similar to 3.7 Angstrom) in both electronic states determined. Several of the bands were assigned as hot bands from the first excited bend-stretch level (K''=1) in the ground electronic state. From the derived A rotational constants, we conclude that the ArCO framework has an approximately T-shaped geometry in both electronic states. The decay lifetime of the upper state of the strongest Ar-HCO band was measured and was found to be somewhat smaller than those previously measured for low rotational levels of free HCO. With the high signal-to-noise ratio in this study, it was also possible to observe transitions in the free (HCO)-C-13 isotopomer. A rotational analysis of the (B) over tilde(2)A'-(X) over tilde(2)A' 0(0)(0) band of the (HCO)-C-13 isotopomer was carried out. The isotopic shifts of the origins of the 3(0)(1) and 2(0)(1) bands were also measured, and a normal mode analysis of HCO(B) was carried out. (C) 1997 American Institute of Physics.