Two-dimensional (2+n) resonance enhanced multiphoton ionization of HCl: State interactions and photorupture channels via low-energy triplet Rydberg states

Abstract

Mass spectra were recorded for (2+n) resonance enhanced multiphoton ionization (REMPI) of HCl as a function of resonance excitation energy in the 81,710-82,870 cm(-1) region to obtain two-dimensional REMPI data. Small but significant fragmentations and H(+), Cl(+), as well as HCl(+) formations are found to occur after resonance excitations to the triplet Rydberg states f (3)Delta(2)(v(') = 0), f (3)Delta(1)(v(') = 0), and g (3)Sigma(+)(1)(v(') = 0). Whereas insignificant rotational line shifts could be observed, alterations in relative ion signal intensities, due to perturbations, clearly could be seen, making such data ideal for detecting and analyzing weak state interactions. Model analysis of relative ion signal intensities, taking account of the major ion formation channels following excitations to Rydberg states, its near-resonance interactions with ion-pair states as well as dissociations and/or photodissociations were performed. These allowed verification of the existence of all these major channels as well as quantifications of the relative weights of the channels and estimates of state interaction strengths. The proposed mechanisms were supported by ion signal power dependence studies.

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.…”