Photofragmentations, state interactions, and energetics of Rydberg and ion-pair states: Two-dimensional resonance enhanced multiphoton ionization of HBr via singlet-, triplet-, Ω 0 and 2 states

Mass spectra were recorded for one-colour resonance enhanced multiphoton ionization (REMPI) of H ⁱBr (i 79, 81) for the two-photon resonance excitation region 79 040-80 300 cm ^-1 to obtain two-dimensional REMPI data. The data were analysed in terms of rotational line positions, intensities, and line-widths. Quantitative analysis of the data relevant to near-resonance interactions between the F ¹Δ ₂(v′ 1) and V ¹Σ ^-(v′ m 7) states gives interaction strengths, fractional state mixing, and parameters relevant to dissociation of the F state. Qualitative analysis further reveals the nature of state interactions between ion-pair states and the E ¹Σ ^- (v′ 1) and H ¹Σ ^-(v′ 0) Rydberg states in terms of relative strengths and J′ dependences. Large variety in line-widths, depending on electronic states and J′ quantum numbers, is indicative of number of different predissociation channels. The relationship between line-widths, line-shifts, and signal intensities reveals dissociation mechanisms involving ion-pair to Rydberg state interactions prior to direct or indirect predissociations of Rydberg states. Quantum interference effects are found to be important. Moreover, observed bromine atom (2 1) REMPI signals support the importance of Rydberg state predissociation channels. A band system, not previously observed in REMPI, was observed and assigned to the k ³Π ₀(v′ 0) ←← X transition with band origin 80 038 cm ^-1 and rotational parameter Bv′=7.238 cm -1.