Multireference singles and doubles configuration interaction study on the electronic states of GaP

Ab initio based multireference singles and doubles configuration interaction (MRDCI) calculations are performed on the ground and low-lying electronic states of GaP using semi-core relativistic effective core potentials and spin-orbit operators. Potential energy curves of 39 Lambda-S states which correlate with three lowest dissociation limits of GaP have been computed. Spectroscopic constants of 17 bound states upto the energy of 47 400 cm(-1) are estimated. The ground state (X(3)Sigma(-)) electronic configuration of GaP is found to be sigma(1)(2)sigma(2)(2)sigma(2)(3)pi(2) with r(e) = 2.5 Angstrom and omega(e) = 268 cm(-1). The best possible dissociation energy (D-e) of the ground stare is calculated to be 39 kcals/mol which is smaller than the available experimental value by 15 kcals/mol. Effects of the spin-orbit coupling On the potential energy curves and spectroscopic constants of those electronic states which correlate with lowest two dissociation limits have been investigated. Spectroscopic properties of the spin-orbit states arising from lowest ten Lambda-S states have been calculated. Electric dipole-allowed transitions like (3)Pi-X(3)Sigma(-), 3(3)Pi-(3)Pi, 2(3)Sigma(+)-(3)Pi, and 2(1)Pi-(1)Pi are found to be more probable. Lifetimes of seven excited states: 4(1)Sigma(+), 2(1)Sigma(+), 2(1)Pi, 2(3)Sigma(+), (3)Sigma(+), 2(3)Pi, and 3(3)Pi are estimated. The 3(3)Pi and 2(3)Sigma(+) states are found to be short-lived with the radiative lifetimes lying between 0.01 and 0.2 mu s. (C) 1999 Elsevier Science B.V. All rights reserved.