Two-dimensional (2+n) resonance enhanced multiphoton ionization of HCl: Photorupture channels via the FΔ21 Rydberg state and ab initio spectra

Abstract

Mass spectra were recorded for (2+n) resonance enhanced multiphoton ionization (REMPI) of HCl as a function of resonance excitation energy in the 82 600-88 100 cm(-1) region to obtain two-dimensional REMPI data. Analysis of ion-mass signal intensities for excitations via the F (1)Delta(2)(v(')=0-2) and the V (1)Sigma(+)(v(')) states as a function of rotational quantum numbers in the intermediate states either revealed near-resonance interactions or no significant coupling between the F (1)Delta(2) and the V (1)Sigma(+) states, depending on quantum levels. Ion-signal intensities and power dependence measurements allowed us to propose photoionization mechanisms in terms of intermediate state involvement. Based on relative ion-signal intensities and rotational line positions we quantified the contributions of Rydberg and valence intermediate states to the photoionization product formation and evaluated coupling strengths for state mixing. Time-dependent density functional theory (TD-DFT), equation-of-motion coupled cluster (EOM-CC), and completely renormalized EOM-CC calculations with various basis sets were performed to derive singlet state potential energy curves, relevant spectroscopic parameters, and to calculate spectra. Experimentally observed spectra and older calculations are compared with the reported ab initio results.

Multiphoton Ionization and Fragmentation of Hydrogen Chloride: A Diatomic Still Good for a Surprise

“…Both groups investigated the ionization/fragmentation pathways through various vibrational bands of the B 1 Σ + (0 + ) state. Very recently, Kauczok et al [22] have reported similar studies on the singlet and triplet Δ states that previously were identified as being in resonance with selected rovibrational states of the B 1 Σ + (0 + ) state [16][17][18].…”

“…The fragmentation ratio (Cl + /HCl + ) does not only show a smooth dependence on the excitation energy, but also crucially depends on the nature of the electronic states as well as on vibrational and rotational quantum numbers [16,18,20]. However, independently of the excitation energy, there exist bands which do not exhibit any significant fragmentation at all.…”

“…It is important to note that the energy of the asymptotic products H + + Cl − lies above the energy of the H + Cl * (4s) system (red solid curve), but below the energy of the H * (n = 2) + Cl system (blue solid curve). It goes without saying that among the omitted bound (red) Rydberg states are several that are characterized by an orbital angular momentum Λ > 0, in particular the F 1 Δ and f 3 Δ states that were shown by Kvaran and coworkers for individual rovibrational levels to be in resonance with rovibrational levels of the B 1 Σ + state [16,18]. F 1 Δ and f 3 Δ states are energetically very close to E 1 Σ + , thus fine-tuning the excitation energy in this narrow energy range allows the experimentalist to access states with differing electronic.…”

“…The colour coding matches that of Figure 3. Recently, Kvaran and coworkers have detailedly studied Rydberg states of HCl with either Λ > 0 or S > 0 (i.e., belonging to the triplet manifold) or both, some of which exhibit near resonances with rovibrational levels of the B 1 Σ + state [16][17][18] Kauczok et al have recently studied the kinetic energy and the angular distributions of these fragments in order to identify those channels which become available to the HCl molecule in the near resonance situation [22]. They have found that those near-resonance rotational levels in the f 3 Δ and F 1 Δ states behave identically to the B 1 Σ + state levels.…”

“…In continuation of their work, Kvaran and coworkers [16][17][18] have investigated several of those states with a predissociation signature by a mass sensitive REMPI timeof-flight technique. Branching ratios for parent molecule ionization and fragmentation producing either H + or Cl + have been studied for both H 35 Cl and H 37 Cl isotopologues on a quantum state selective basis.…”