REMPI spectra of IBr: Vibrational and rotational analysis of the b[²Π_1/2]_c6s;1 Rydberg states of I⁷⁹Br and I⁸¹Br

Partly rotationally resolved (2 + 1) resonance-enhanced multiphoton ionization spectra of the vibrational bands corresponding to the b[²Π_1/2]_c6s;1 ← X transitions in IⁱBr (i = 79, 81) for the natural abundance of isotopes have been recorded at room temperature. Vibrational bands consist of contributions from both isotopomers with varying degrees of overlap depending on vibrational quantum numbers. The band spectra were analyzed by simulation calculation. Rotational constants (B̄_ν′ and D̄_ν′) and corresponding internuclear distances (r_ν′) for the Rydberg state (b[²Π_1/2]_c6s;1) were obtained, as well as equilibrium position rotational parameters. Thus for I⁷⁹Br, B_e′ = 0.061 61 ± 0.000 05 cm^-1, α_e′ = (2.2 ± 0.1) × 10^-4 cm^-1 and r_e′ = 2.371 ± 0.002 Å. Vibrational analysis based on the determination of band origins from the spectral simulations were performed to obtain ω_e′ = 307.4 ± 0.5 cm^-1, ω_eχ_e = 1.0 ± 0.1 cm^-1 for I⁷⁹Br, and T_e′ = 56 362 cm^-1. Spectroscopic parameters for I⁸¹Br are derived from the ones for I⁷⁹Br in a standard way (see text). Perturbation due to interaction between the Rydberg state and an ion-pair state is considered.