Vibrational and rotational structure in the He I-excited photoelectron spectrum of the A 2 Sigma 1/2+ state of HBr+

Ab initio investigation of Br-3d core-excited states in HBr and HBr+ toward XUV probing of photochemical dynamics

Ultrafast X-ray/XUV transient absorption spectroscopy is a powerful tool for real-time probing of chemical dynamics. Interpretation of the transient absorption spectra requires knowledge of core-excited potentials, which necessitates assistance from high-level electronic-structure computations. In this study, we investigate Br-3d core-excited electronic structures of hydrogen bromide (HBr) using spin-orbit general multiconfigurational quasidegenerate perturbation theory (SO-GMC-QDPT). Potential energy curves and transition dipole moments are calculated from the Franck-Condon region to the asymptotic limit and used to construct core-to-valence absorption strengths for five electronic states of HBr (Σ 1 0 + ,   3 Π 1 ,   1 Π 1 ,   3 Π 0 + ,   3 Σ 1 ) and two electronic states of HBr+ (2Π3∕2, 2Σ1∕2). The results illustrate the capabilities of Br-3d edge probing to capture transitions of the electronic-state symmetry as well as nonadiabatic dissociation processes that evolve across avoided crossings. Furthermore, core-to-valence absorption spectra are simulated from the neutralΣ 1 0 + state and the ionicΠ 2 1 / 2 , 3 / 2 states by numerically solving the time-dependent Schrödinger equation and exhibit excellent agreement with the experimental spectrum. The comprehensive and quantitative picture of the core-excited states obtained in this work allows for transparent analysis of the core-to-valence absorption signals, filling gaps in the theoretical understanding of the Br-3d transient absorption spectra.

Bond-dissociation energies of cations--pushing the limits to quantum state resolution

Currently available concepts for measuring the bond-dissociation energy of cations D(o) are reviewed. Starting from the traditional approach of directly measuring the threshold energy for the appearance of fragment ions, attention is directed towards indirect measurements, where threshold energies are obtained by extrapolation of, for example, rate constants k(E) or kinetic energy release (KER) data to the threshold of interest. More recent high precision techniques again utilize direct measurements, for example, of the disappearance energy of the parent ion. Most precise data are obtained from quantum state resolved measurements of the dissociation energy, where the threshold energy is bracketed by the existing quantum states above and below the threshold. Ultimately the limits can even be pushed beyond the bracketing limit, by investigating steps on the lineshape of homogeneously broadened single rotational transitions.

Rotational State Distribution of HBr+ Ions Formed by Resonance Enhanced Multiphoton Ionization

The rotational state distribution of HBr+ ions formed via a large number of pump lines in the f 3Δ2 ← 1Σ and the F 1Δ2 ← 1Σ REMPI spectrum has been derived from the analysis of state-selective predissociation spectra. For most pump lines in the two REMPI spectra molecular ions are formed in narrow state distributions with dominant contributions of two or three different rotational states. By choice of the appropriate pump line in the REMPI spectrum this state distribution can be shifted from N = 0 to about N = 10. The data provide evidence that REMPI spectroscopy is a viable tool for the formation of state-selected molecular ions.