Rydberg and valence state excitation dynamics: a velocity map imaging study involving the E–V state interaction in HBr

Abstract

Photoexcitation dynamics of the E((1)Σ(+)) (v' = 0) Rydberg state and the V((1)Σ(+)) (v') ion-pair vibrational states of HBr are investigated by velocity map imaging (VMI). H(+) photoions, produced through a number of vibrational and rotational levels of the two states were imaged and kinetic energy release (KER) and angular distributions were extracted from the data. In agreement with previous work, we found the photodissociation channels forming H*(n = 2) + Br((2)P3/2)/Br*((2)P1/2) to be dominant. Autoionization pathways leading to H(+) + Br((2)P3/2)/Br*((2)P1/2) via either HBr(+)((2)Π3/2) or HBr(+)*((2)Π1/2) formation were also present. The analysis of KER and angular distributions and comparison with rotationally and mass resolved resonance enhanced multiphoton ionization (REMPI) spectra revealed the excitation transition mechanisms and characteristics of states involved as well as the involvement of the E-V state interactions and their v' and J' dependence.

State interactions and illumination of hidden states through perturbations and observations of new states: High energy resonance enhanced multiphoton ionization of HI

“…We wish to use these expressions to replace the less clear expressions "nearresonance-" and "off-resonance-" interactions, respectively, which have been used before. 29,[31][32][33]39,[44][45][46]58,61 Interactions between Rydberg and ion-pair states of the hydrogen halides appear distinctively as perturbations in rotationally resolved REMPI spectra, i.e., as deviations in the expected spectral structure of unperturbed states. These deviations can show as line shifts (LS-effects) as a result of the energy level shifts and/or as line-intensity alterations (LI-effects) due to the state mixing which can cause alterations in ion formation paths.…”

“…Hence, the energy spacing between J ′ levels (∆E J ′ , J ′ −1 ) for the Rydberg states is larger than corresponding levels for the ion-pair states. [31][32][33][44][45][46]58,61,62 Therefore, near-degenerate interactions, for ∆E J ′ ≈ 0, typically, are observed for one or two J ′ levels only, whereas non-degenerate interactions can be observed for a range of J ′ levels both to higher and lower energies with increasing |∆E J ′| as J ′ deviates further away from the near-degenerate levels. 62 Therefore, the nondegenerate interactions show as gradually decreasing LS-and LI-effects, as the J ′ s deviate further away from the neardegenerate J ′ s.…”

“…Furthermore, some REMPI coupled velocity map imaging (VMI) studies have been performed on the hydrogen halides, highlighting various photoionization and photofragmentation pathways. [46][47][48][49][50][51][52] The large atomic mass of iodine makes HI particularly interesting amongst the hydrogen halides due to its strong spin-orbit interactions. For the lighter hydrogen halides, such as HF and HCl, the spin and electronic orbital motions are coupled strongly to the molecular axis to give well defined projections on the internuclear axis, which along with the angular momentum of the nuclear motion (R) give the total angular momentum, J according the to Hund's case (a) classification.…”

High energy state interactions, energetics and multiphoto-fragmentation processes of HI

“…This is along the same lines as our findings for the corresponding HBr # superexcited states involved in (2 + n ) REMPI of HBr in the case of H + formation. 18,57,58…”

“…This is due to their heavy (halogen atoms) vs. light (hydrogen) fragment particle combination which generally results in highly resolvable rotational spectral structures and a relatively clear distinction between different perturbation effects of Rydberg and valence states. 1–21 In this respect hydrogen iodide (HI), with its large iodine atom mass, is particularly interesting. A large number of Rydberg and ion-pair vibrational states (HI**) have been assigned and characterized both in absorption 21–23 and resonance enhanced multiphoton ionization (REMPI) 24–30 for the excitation energy region of about 66 000–75 000 cm −1 .…”