State Selective Predissociation Spectroscopy of Hydrogen Bromide Ions (HBr⁺) via the ²Σ⁺ ← ²Π_i(i=1/2, 3/2) Transition

Abstract

The photodissociation of hydrogen bromide ions (HBr + ) has been investigated via the 2 Σ + (V′)1, 2, 3, and 4) r 2 Π i (i)1/2, 3/2, V′′)0) transitions. The spectra reveal that state selective photodissociation with complete resolution of the rotational, orbital, and spin angular momentum as well as the parity of the HBr + ions is possible in the 2 Σ + (V′)1, 2). The analysis of the spectra yields the rotational constants, the spin-rotation coupling constant, and the orbit-rotation coupling constant in the respective electronic states. All angular momentum eigenstates of the 2 Σ + (V′)2) state (and of all higher vibrational states) predissociate. The first eigenstate in the 2 Σ + (V′)1) state that predissociates is the J′ ) 25/2, R′ ) 12 state. The lifetime of HBr + is found to decrease significantly with increasing vibrational excitation in the 2 Σ + state. Within the experimental error limits no J dependence of the lifetime is observed.

Inhibition of hydrogen oxidation by HBr and Br2

“…1983, ∆ f H , have been adopted without further scrutiny by virtually all subsequent thermochemical tabulations. For gaseous Br 2 (the formation enthalpy of which is equivalent to the vaporization enthalpy of condensed-phase bromine corrected for ideal vs. real behavior) there are indeed no relevant measurements since the evaluation of Cox et al However, for Br and HBr, there are several newer determinations that can potentially improve and/or modify the thermochemistry of these two "key" species, such as, for example, the analysis of spectroscopic data by Gerstenkorn and Luc [52] leading to a refined value of D 0 (Br 2 ), or the spectroscopic determination of predissociation of HBr + [53] that allows access to D 0 (HBr) via a positive ion cycle. Thus, the current ATcT value for Br (unchanged from the value in the very recently given interim set of ATcT enthalpies of formation of several atoms [45]; enthalpy of formation at 298.15 K of 111.85±0.06 kJ mol −1 , while confirming the original CODATA value [51], is actually more accurate by a factor of two.…”

Unimolecular Reactions in Molecular Ions and Cluster Ions — From Thermal Towards State-Selective Experiments

“…the laser linewidth, Doppler broadening, Stark effect and nuclear-electronic spin coupling. 111 In the case of the v' = 2 state in the 2E+ the experimentally observed linewidth is independent of the rotational quantum number. A significant contribution to the experimental linewidth most likely stems from the nuclear-electronic spin coupling (about 0.2 cm 1) which is known from infrared laser spectroscopy of the ion ground state.…”

Bond‐dissociation energies of cations—Pushing the limits to quantum state resolution

“…Evidently, REMPI spectroscopy is a powerful tool for rovibrational state selection of molecular ions, as has been reviewed by Anderson (1992). The author's group has demonstrated state selection of HBr þ and HCl þ ions over a wide range of rotational quantum numbers (Penno, Holzwarth, & Weitzel, 1998Michel, Korolkov, & Weitzel, 2004;Penno & Weitzel, 2004). In general molecular ions are formed with a finite, albeit very narrow, rotational distribution, with predominant contribution from two rotational eigenstates.…”

“…This bound A state is crossed by three repulsive electronic states ð 4 AE À ; 2 AE À ; 4 PÞ, coupling to which leads to predissociation above a certain quantum state in the A state at the dissociation limit of the X state. Consequently optical (rovibronic) excitation of ground state HBr þ ions into the A 2 AE þ state opens access to predissociation in the region of the threshold of fragmentation (Penno, Holzwarth, & Weitzel, 1998;Penno & Weitzel, 2004). From photoelectron spectroscopy it was known that the A 2 AE þ (v ¼ 2) state predissociates fast for all rotational eigenstates (Baltzer et al, 1994;Yencha et al, 1998).…”

“…For N ¼ 12 this splitting amounts to 11.31 cm À1 . In summary this represents a bracketing of the true molecular dissociation energy, which must be located in between these two Penno, Holzwarth, and Weitzel (1998) (Nizkorodov et al, 1997;Bieske & Dopfer, 2000). The dissociation energy was reported as D o ¼ 2781.5 AE 1.5 cm since the rotational constants are larger and the separation of rotational states is consequently also larger compared to the Ar À HN þ 2 ion.…”