SPIN-ORBIT TYPE PERTURBATIONS IN THE B(1)(1)PI STATE OF SCCL - CHARACTERIZATION OF THE INTERACTING (1)(3)SIGMA(+) STATE

An extensive study of the B(1)(1) Pi --> X(1) Sigma(+) system of (ScCl )-Sc-45-Cl-35 and (ScCl)-Sc-45-Cl-37 observed in high resolution spect ra of the molecular thermal emission is presented. The rotational anal ysis reveals the presence of localized perturbations in almost all bra nches of bands with upsilon' less than or equal to 5, associated with hyperfine broadening of the perturbed Q lines. These effects are inter preted as consequences of the avoided crossing between B(1)(1) Pi(upsi lon) and (1)(3) Sigma(+)(upsilon + 2) levels due to spin-orbit interac tion. It appears possible to enter the interacting levels for both iso topomers in the same matrix representation, the energy term elements o nly involving equilibrium parameters of the states (isotopically scale d to (ScCl)-Sc-45-Cl-35). A semideperturbed model of the interacting s tates, taking account of the (upsilon similar to upsilon + 2) perturba tions only, is first envisaged. The simultaneous fit of some 6600 line wavenumbers in 17 bands for (ScCl)-Sc-45-Cl-35 and 7 bands for (ScCl) -Sc-45-Cl-37 With a total standard deviation of 0.005 cm(-1) makes it possible to characterize the (1)(3) Sigma(+) state and precisely descr ibe B(1)(1) Pi from upsilon = 0 to upsilon = 5. Spin-orbit interaction parameters xi(u,v+2) are determined. A full deperturbation is then ca rried out using a model describing the levels upsilon = 0 to upsilon = 7 of (ScCl)-Sc-45-Cl-35 and upsilon = 0 to upsilon = 4 of (ScCl)-Sc-4 5-Cl-37 for the two states, and taking account of all significant inte ractions. The following principal equilibrium molecular constants (in cm(-1)) are obtained: -for (1)(3) Sigma(+), T-e = 5388.23, omega(e) = 367.57, omega(e)x(e) = 1.29, B-e = 0.15550, alpha(e) = 0.00081, 10(6)D (e) = 0.111; -for B(1)(1) Pi T-e = 6016.09, omega(e) = 381.89, omega(e )x(e) = 1.37, B-e = 0.15511, alpha(e) = 0.00079, 10(6)D(e) = 0.103. Th e vibration-independent spin-orbit interaction parameter is directly d etermined, xi(el) = 53.02 cm(-1). (C) 1996 Academic Press, Inc.