LASER SPECTROSCOPY OF THE LANTHANIDE MONOFLUORIDES - ANALYSIS OF THE A(2)PI-X(2)SIGMA(+) TRANSITION OF YTTERBIUM MONOFLUORIDE

High-resolution excitation spectra have been obtained of several bands in the A(2) Pi-X(2) Sigma(+) transition of (YbF)-Yb-172, (YbF)-Yb-174 , and (YbF)-Yb-176. Vibrational, rotational, and spin-rotation constan ts have been determined for the ground X(2) Sigma(+) state of the thre e isotopomers. The vibrational frequency, omega(c) = 505.6581(91) cm(- 1), of (YbF)-Yb-174, the most abundant isotopomer, confirms the assign ment of this state to the Yb+(4f(14)6sF- configuration. Vibrational sp acings and rotational, spin-orbit, and lambda doubling constants have been calculated for the A(2) Pi. state, which is heavily perturbed. Tw o vibrational levels of a new Omega = 0.5 state have been observed in the vicinity of the A(2) Pi(1/2) state and analysis of the rotational structure and lambda (or omega) doubling of these levels indicates tha t this is the perturbing state. Analysis of the isotope structure esta blishes the vibrational numbering of the two levels as upsilon = 0 and 1. The deperturbed vibrational spacing in this state is calculated to be similar to 605 cm(-1) and suggests that the state originates in th e Yb+(4f(13)6s(2)F- configuration. The lambda doubling in the A(2) Pi( 1/2) stare, originating in the Yb+(4f(14)6p) configuration, is examine d in terms of its interaction with the B-2 Sigma(+) state, which comes from the same configuration. Discrepancies between observed and calcu lated values, especially for A(2) Pi(1/2) upsilon = 1, provide further evidence for the perturbation. (C) 1995 Academic Press, Inc.