Infrared Stark and Zeeman spectroscopy of OH–CO: The entrance channel complex along the OH + CO → trans-HOCO reaction pathway

Abstract

Sequential capture of OH and CO by superfluid helium droplets leads exclusively to the formation of the linear, entrance-channel complex, OH-CO. This species is characterized by infrared laser Stark and Zeeman spectroscopy via measurements of the fundamental OH stretching vibration. Experimental dipole moments are in disagreement with ab initio calculations at the equilibrium geometry, indicating large-amplitude motion on the ground state potential energy surface. Vibrational averaging along the hydroxyl bending coordinate recovers 80% of the observed deviation from the equilibrium dipole moment. Inhomogeneous line broadening in the zero-field spectrum is modeled with an effective Hamiltonian approach that aims to account for the anisotropic molecule-helium interaction potential that arises as the OH-CO complex is displaced from the center of the droplet.

VUV photochemistry of the H2O⋯CO complex in noble-gas matrices: formation of the OH⋯CO complex and the HOCO radical

“…the directions of the shifts are opposite in comparison with those of OHÁ Á ÁCO. 38,43,45 Thus, it seems that the less stable OHÁ Á ÁOC structure is not stabilized under our experimental conditions. It is worth noting that this result is in agreement with the studies in the gas-phase and He droplets, where only the OHÁ Á ÁCO structure was detected.…”

“…The obtained data are in good agreement with the calculations reported previously. 38,43,45 No evidence for the stabilization of the less stable OHÁ Á ÁOC structure was found. The formation of the OHÁ Á ÁCO complex is quite efficient in Ne and Ar matrices, and it is hardly visible in the Xe matrix.…”

“…44 Very recently, Brice et al have reported the OH fundamental frequency of the OHÁ Á ÁCO complex in He droplets at 3551 cm À1 (shifted by À17 cm À1 with respect to the OH monomer). 45 Nevertheless, full experimental characterization of the fundamental IR absorptions of the OHÁ Á ÁCO complex is still lacking. † Another species that is relevant to this system is the carboxyl radical (HOCO) that is separated from the OHÁ Á ÁCO complex by a low energy barrier (a few hundred cm À1 ).…”

Infrared Spectroscopy of Molecular Radicals and Carbenes in Helium Droplets

“…4.1c) that allows us to perform Stark spectroscopy measurements by applying a static electric field (0 to 80 kV/cm) to electrodes that surround the droplet beam/laser interaction region. The use of various Stark field strengths and laser polarization orientations (leading to different selection rules), allows us to accurately determine dipole moments of He-solvated species [21,41,44,65,66]. For example, the experimental (black) and simulated (red) Stark spectra of the linear OH-CO complex are shown in Fig.…”

“…For example, the experimental (black) and simulated (red) Stark spectra of the linear OH-CO complex are shown in Fig. 4.6 [44]. The zero-field spectrum is shown along the bottom of the figure, and the Stark spectra recorded at three different field strengths provide the dipole moments of the complex in both the ground and excited OH stretch vibrational states.…”