FINE AND HYPERFINE-STRUCTURE IN THE VIBRATIONAL-SPECTRUM OF THE CHI(2)PI STATE OF HBR+

The infrared spectrum of HBr+ in the (2) Pi(1/2) and (2) Pi(3/2) spin substates of the ground electronic state has been investigated between 1975 and 2360 cm(-1) using a tunable diode laser spectrometer coupled to an ac glow discharge cell. Both fine and hyperfine studies have be en carried out. In the former, about 300 vibration-rotation transition s were measured for each of the isotopomers (HBr+)-Br-79 and (HBr+)-Br -81. These belonged to the five bands (upsilon'-upsilon'') = (1-0) to( 5-4). The linewidth was similar to 0.006 cm(-1). In this inverted (2) Pi state, the difference (\A(c)\ - omega(e)) is small (similar to 200 cm(-1)) compared to omega(e) (2440 cm(-1)). Here A(e) and omega(e) are the equilibrium values of the spin-orbit constant and the harmonic vi brational frequency, respectively. As a result, the energy levels occu r in neighboring, but nonresonant, pairs with (upsilon, (2) Pi(3/2)) c oupled to (upsilon - 1, (2) Pi(1/2)). The one exception is the (2) Pi( 3/2) state with upsilon = 0, which is isolated. Centrifugal distortion matrix elements between partner states have been shown to effect sign ificantly the Lambda-doubling. A model has been developed in which the se distortion matrix elements are treated by a vibrational Van Vleck t ransformation carried to third order. A good fit has been obtained wit hout introducing any variable parameters to characterize the (Delta up silon not equal 0; Delta Omega = +/-1) effects. Equilibrium values wer e determined for the principal parameters which characterize the indiv idual vibrational levels. In the hyperfine study, a combined total of 57 hyperfine transitions were observed in the two spin substates of (H Br+)-Br-79. An equal number were measured for (HBr+)-Br-81. These were distributed over the P, Q, and R branches of the four lowest vibratio nal bands. The matrix elements for the magnetic dipole and electric qu adrupole interactions have been written in the e/f symmetrized scheme more commonly used in vibration-rotation problems. Values have been ob tained for the Frosch-Foley magnetic hyperfine constants a, c, and d b y using the value of b determined by Lubic el al., J. Mol. Spectrosc. 131, 21-31 (1989). These results have been used to investigate the ele ctronic properties of the ion. The analysis supports a model in which the electron distribution is close to that of a bromine atom perturbed by a proton. (C) 1995 Academic Press, Inc.