REMPI SPECTRA OF IBR - VIBRATIONAL AND ROTATIONAL ANALYSIS OF THE B[(2)PI(1 2)](C)6S-1 RYDBERG STATES OF (IBR)-BR-79 AND (IBR)-BR-81/

Partly rotationally resolved (2 + 1) resonance-enhanced multiphoton io nization spectra of the vibrational bands corresponding to the b[(II1/ 2)-I-2](c)6s;1 <-- X transitions in (IBr)-Br-i (i = 79, 81) for the na tural abundance of isotopes have been recorded at room temperature. Vi brational bands consist of contributions from both isotopomers with va rying degrees of overlap depending on vibrational quantum numbers. The band spectra were analyzed by simulation calculation. Rotational cons tants (($) over bar B-v' and ($) over bar D-v') and corresponding inte rnuclear distances (r(v')) for the Rydberg state (b[(II1/2)-I-2](c)6s; 1) were obtained, as well as equilibrium position rotational parameter s. Thus for (IBr)-Br-79, B-e' = 0.061 61 +/- 0.000 05 cm(-1), alpha(e) ' = (2.2 +/- 0.1) x 10(-4) cm(-1) and r(e)' = 2.371 +/- 0.002 Angstrom . Vibrational analysis based on the determination of band origins from the spectral simulations were performed to obtain omega(e)' = 307.4 /- 0.5 cm(-1), omega(r)x(e) = 1.0 +/- 0.1 cm(-1) for (IBr)-Br-79 and T -e' = 56 362 cm(-1). Spectroscopic parameters for (IBr)-Br-81 are deri ved from the ones for (IBr)-Br-79 in a standard way (see text). Pertur bation due to interaction between the Rydberg state and an ion-pair st ate is considered.