Ab initio configuration interaction study of the predissociation of the (4s), (4p sigma) (1,3)Pi, and (4p pi) (3)Sigma(+) Rydberg states of HCl and DCl

Ab initio configuration interaction (Cl) calculations are carried out for t he lowest-lying six (1,3)Pi and three (3)Sigma(+) states. In addition, the first and second radial couplings <phi(i)(R,r)parallel to partial derivativ e/partial derivative R\phi(j)(R,r)> and <phi(i)(R,r)\partial derivative(2)/ partial derivative R-2\phi(j)(R,r)>, spin-orbit, and rotational couplings a re also evaluated based on the resulting highly correlated wave functions. Energy positions and predissociation linewidths of rovibrational levels ass ociated with the above electronic states are determined in the adiabatic re presentation by means of the complex scaling method employing a basis of co mplex scaled Hermite polynomials and Gauss-Hermite quadrature. The present treatment correctly reproduces a number of observed trends in energy and li ne broadening for individual rovibrational levels of the (4s)b (3)Pi and C (1)Pi states of HCl and DCl. The calculated linewidths for the v=0, J=2, an d J=8 rovibrational levels of the (4s)C (1)Pi state of HCl are 1.2 and 2.1 cm(-1), respectively, which is in good agreement with the recently observed rotational dependence of line broadening for the v=0 level of this state [ M. H. Alexander , Chem. Phys. 231, 331 (1998)]. The present calculations fi nd that the linewidths of the (4p sigma)D (1)Pi state are greater than for the (4p sigma)d (3)Pi state. The distinctive predissociation mechanisms of the D (1)Pi and the d (3)Pi states are discussed on the basis of the calcul ated radial couplings. The calculations predict very broad lines for the v= 0 and 1 vibrational levels of the lowest adiabatic bound (3)Sigma(+) state, consistent with the fact that the corresponding state has not yet been ide ntified by spectroscopic means. (C) 2000 American Institute of Physics. [S0 021-9606(00)31301-0].