Improvement of the spectroscopic constants of the PF(A(3)Pi) state and assignment of the PF(A-X) transition dipole function

High-resolution laser-excitation spectra were acquired for the v' = 3-7 lev els of the PF(A(3) Pi (0.1.2) <-- X-3<Sigma>(-)) transition from PF(X(3)Sig ma (-)) molecules generated in a discharge flow reactor. These results were combined with lower resolution excitation spectra for the v' = 8-11 levels and with existing high-resolution data in the literature for v' = 0 and 1 to assign improved spectroscopic constants for PF(A(3)Pi (0.1.2)). The abno rmal vibrational energy level spacings for all spin components of the PF(A( 3)Pi) state are evidence for a homogeneous interaction with another (3)Pi s tate. The Lambda -doublet separation in the PF((3)Pi (0),) substate increas es with vibrational level, which is taken as evidence for interaction with the PF(b(1)Sigma (+)) state. Laser-induced fluorescence spectra from indivi dual v' = 0-5 levels were used to obtain vibrational band intensities of th e A-X transition. The strong dependence of the transition dipole on the r-c entroid is consistent with the reduction in the radiative lifetimes with in creasing v' level. The similarity between the isovalent PF(A(3)Pi) and SO(A (3)Pi) states is noted and the bond dissociation energy of PF(X(3)Sigma (-) ) is discussed. (C) 2001 Academic Press.