Resonance-Enhanced Multiphoton Ionization of CH₂Br₂: Rydberg States, Photofragmentation, and CH Spectra

Abstract

Mass-resolved (2 + n) resonance-enhanced multiphoton ionization (REMPI) spectra of CH2Br2 in the two-photon resonance excitation region from 71 200 to 82 300 cm(-1) were recorded and analyzed. Spectral structures allowed characterization of new molecular Rydberg states. C*((1)D2) was found to be an important intermediate in the photodissociation processes. A broad spectral feature peaking at about 80 663 cm(-1) in the C(+) spectrum and frequently seen in related studies is reinterpreted and associated with switching between three- and two-photon ionization of C*((1)D2). Analysis of band structures due to transitions from the A(2)Δ state of CH* that were seen in the CH(+) and C(+) REMPI spectra allowed characterization of three electronic states of CH, assigned as E(2)Π, D(2)Π, and F(2)Σ(+), which clarifies a long-term puzzle concerning the energetics of the CH radical. Predissociation of the E, D, and F states to form C*((1)D2) occurs. Bromine atomic lines were observed and are believed to be associated with bromine atom formation via predissociation of CH2Br2 Rydberg states.

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

“…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.…”

“…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.…”

“…Thus, for weakly interacting states, there may be a distinctive lack of LS-effects, whereas significant LIeffects may be observed. 31,32,45,61…”

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

“…b) Weak near-resonance state interactions, distinguishable by localized line shifts, (hence energy level shifts), as well as alterations in signal line intensities, 19,22 observed for singlet states and > 0 state interactions. c) Medium to strong off-resonance state interactions, distinguishable by large scale line/energy level shifts, as well as alterations in signal intensities, 22,24 observed for triplet and singlet states and = 0 state interactions.…”

Photofragmentation Pathways for Gas-Phase Lanthanide Tris(isopropylcyclopentadienyl) Complexes

“…There have been many studies on the photofragmentation pathways of gas-phase molecular compounds, − metal–organic complexes, − and clusters. , Recently, our group reported the unimolecular gas-phase photodissociation mechanisms of lanthanide tris­(η 5 -cyclopentadienyl) complexes, Ln­(Cp) 3 , and lanthanide tris­(tetramethylcyclopentadienyl) complexes, Ln­(TMCp) 3 , through both experimental photoionization time-of-flight mass spectrometry (PI-TOF-MS) and theoretical atomistic simulation of the fragmentation dynamics . It was hypothesized that two types of reaction pathways dominate in the photofragmentation of both Ln­(Cp) 3 and Ln­(TMCp) 3 precursors: intact ligand stripping, leading to the production of bare metal, and ligand cracking within the metal–ligand complex, giving rise to metal carbide and metal hydrocarbide compounds.…”