The structure of the lowest electronic Rydberg state of CdAr complex determined by laser double resonance method in a supersonic jet-expansion beam

Abstract

The lowest E1( 3Σ +) Rydberg state of the CdAr van der Waals (vdW) complex was investigated by means of an optical–optical double resonance (OODR) method of laser spectroscopy in conjunction with a free jet-expansion molecular beam. Two dye lasers were employed for the two-step excitation. The A0 +( 3Π +) and B1( 3Σ +) states were used as intermediates in the excitation process from the X0 +( 1Σ +) ground state. Two types of bound–bound excitation spectra of the E1←A0 + and E1←B1 transitions were recorded indicating the existence of two, well defined minima in the E1-state potential energy (PE) curve. First, considerably deep, with the well depth of D e′(E1 2)=1309.0 cm −1 and second, separated by a positive PE barrier, with D e′(E1 2)=24.2 cm −1. Combination of bound–bound and first-time observed bound-free excitation spectra enabled a complete determination of the spectroscopical parameters of the PE curve of the E1-Rydberg state, the height of the PE barrier and its approximate location. In the excitation spectra of the E1←B1 transition, a nodal structure of the bound-free transitions was observed and elucidated by a projection of the B1-state vibrational wave-functions onto the E1-state potential barrier and/or onto the repulsive part of the E1-state PE curve. The experimental results of our investigation coincides well with recently published results of ab initio calculation of Czuchaj and co-workers [Chem. Phys. 248 (1999) 1; Chem Phys. 263 (2001) 7; Theor. Chem Acc. 105 (2001) 219].