Transition properties of the spin- forbidden a 4 Π-X 2 Π systems in the NO, PO and PS molecules

The potential energy curves (PECs) for six low-lying states corresponding to the first dissociation limit ( 4 S u + 3 P g ) of the NO, PO, and PS molecules are calculated by the multireference configuration interaction (MRCI) method. The X 2 Pi -a 4 Pi band is the focus of this work. By introducing the spin-orbit coupling (SOC) with Breit -Pauli operator via state-interacting technique, the PECs and wavefunctions compositions of Omega states are obtained. Based on the Lambda -S states composition of the corresponding Omega states and the calculated electric-dipole transition moments between Lambda -S state, we present intensity of the spin-forbidden quartet-doublet bands. Spectroscopic constants for all sub-bands of the a 24 Pi 3/2 , a 3 4 Pi 1/2 , a 4 4 Pi 1/2 -> X 1 2 Pi 1/2 and a 1 4 Pi 5/2 , a 2 4 Pi 3/2 , a 3 4 Pi 1/2 , a 4 4 Pi 1/2 -> X 2 2 Pi 3/2 systems of the NO, PO, and PS are estimated. A set of transition parameters of these sub-bands are given. The present results are supposed to provide a significant supplement for the spin-forbidden a 4 Pi -> X 2 Pi band origins of the astrophysically important NO, PO, and PS molecules.