Spectroscopic observation of the preferentially stabilized, linear He⋯ICl(X 1Σ+) complex

Abstract

Stabilization and rovibronic spectra of the T -shaped and linear ground-state conformers of a weakly bound raregas-homonuclear dihalogen complex: He Br 2He 79 Br 2 B,v=8←X,v ″ =0 excitation spectrum: Ab initio prediction and spectroscopic manifestation of a linear isomer Spectroscopic features attributed to rovibronic transitions from both the T-shaped and linear He¯I 35 Cl(X) and He¯I 37 Cl(X) ground-state complexes have been recorded in the ICl B 3 ⌸ 0ϩ -X 1 ⌺ ϩ , 2-0 and 3-0 spectral regions using laser-induced fluorescence spectroscopy. Experiments performed using varying expansion conditions indicate that the He¯I 35,37 Cl(X) complex with a linear equilibrium orientation lies lower in energy than the separately localized T-shaped isomer even though the transition energies of the T-shaped and linear complexes are shifted by ϳ3.5 and ϳ14 cm Ϫ1 to higher energy than the I 35,37 Cl B -X band origins, respectively. Based on comparison with the excited state theoretical predictions of Waterland et al. ͓J. Chem. Phys. 92, 4261 ͑1990͔͒, estimates of the binding energies for the ground state T-shaped and linear He¯I 35 Cl(X) complexes are 17 and 21 cm Ϫ1 , respectively, in qualitative agreement with the recently published predictions of 15.2 and 18.3 cm Ϫ1 obtained using high level ab initio theory for the ground state potential energy surface ͓J. Chem. Phys. 117, 7017 ͑2002͔͒.

Combined experimental/theoretical investigation of the He+ICl interactions. I. Rovibronic spectrum of He⋯ICl complexes in the ICl B–X, 3–0 region

“…26 A pulsed supersonic expansion of ICl entrained in a helium carrier gas maintained at 80 or 200 psi was used to stabilize the weakly bound complexes. An excitation laser intersected the expansion with a beam diameter of 3 mm at a specific distance downstream from the pulsed valve orifice.…”

“…25,26 One band is observed just to the blue of each monomer band. In accord with the accepted trends, it is attributed to transitions of the T-shaped complex.…”

“…25,26 Subsequent high-level theoretical calculations of the He¯Br 2 spectra 27,28 provide strong evidence that the higher energy He¯Br 2 band can be attributed to transitions of a linear He¯Br 2 (X,vЉϭ0) isomer to He¯Br 2 (B,vЈ) states with intermolecular vibrational excitation. 27,28 The initial simulations of the higher energy He¯ICl feature 26 were undertaken using rigid rotor models. 29,30 These simulations consistently underpredicted the number of rotational lines observed in the experimental spectrum, especially at higher transition energies in the band.…”

“…The presence of additional He¯I 35,37 Cl or higher-order He n¯I 35,37 Cl LIF bands overlapping in this energy region as well as K-type doubling of rotor lines and Coriolis effects on transition energies were proposed as possible sources of discrepancies between the simulations and the experimental data. 26 Although a satisfactory fit was not obtained, the rigid rotor simulations did indicate that it was necessary to invoke a linear geometry in the ground and excited states in order to obtain the overall shape of the band. Even though the structure could be either He¯I-Cl or He¯Cl-I, intuition would suggest that the He¯I-Cl would be favored since the attraction between the helium atom and the electropositive iodine atom would be greater than between the helium and the chlorine.…”

Stark Field Control of Nonadiabatic Dynamics in Triatomic Hydrogen

“…In polyatomic systems the larger number of degrees of freedom complicates the observation and description of dynamical properties [2]. During the last decade powerful experimental techniques have been brought to bear on nonadiabatic processes: Ultrafast lasers make it possible to follow the course of a chemical reaction [3][4][5], molecular beam technology allows the quantum state preparation of reactants as well as the state selective detection of products [6][7][8], and novel multidimensional coincidence measurements provide hitherto inaccessible information about vector correlations in molecular dynamics [9][10][11][12].…”