Paul L. Raston

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

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.

FAR-INFRARED SPECTROSCOPY OF THE H2-O2 VAN DER WAALS COMPLEX

We report the far infrared spectrum of H2-O2 at 80 K in the vicinity of the pure rotational bands of H2. Sharp peaks were observed, which correspond to end-over-end rotational transitions of the H2-O2 molecular complex, that are superimposed over broad collision induced absorptions. We find that the maximum value of the end-over-end rotational quantum number that is bound is seven, which is two more than supported by a recently reported ab initio H2-O2 potential energy surface. The rotational spectrum reported here should therefore greatly help in refining this surface, which is used to calculate scattering processes relevant to the chemistry occurring in interstellar molecular clouds.

Microwave spectroscopy of the seeded binary and ternary clusters CO-(pH2)2, CO-pH2-He, CO-HD, and CO-(oD2)N=1,2

We report the Fourier transform microwave spectra of the a-type J = 1-0 transitions of the binary and ternary CO-(pH2)2, CO-pH2-He, CO-HD, and CO-(oD2)N=1,2 clusters. In addition to the normal isotopologue of CO for all clusters, we observed the transitions of the minor isotopologues, (13)C(16)O, (12)C(18)O, and (13)C(18)O, for CO-(pH2)2 and CO-pH2-He. All transitions lie within 335 MHz of the experimentally or theoretically predicted values. In comparison to previously reported infrared spectra [Moroni et al., J. Chem. Phys. 122, 094314 (2005)], we are able to tentatively determine the vibrational shift for CO-pH2-He, in addition to its b-type J = 1-0 transition frequency. The a-type frequency of CO-pH2-He is similar to that of CO-He2 [Surin et al., Phys. Rev. Lett. 101, 233401 (2008)], suggesting that the pH2 molecule has a strong localizing effect on the He density. Perturbation theory analysis of CO-oD2 reveals that it is approximately T-shaped, with an anisotropy of the intermolecular potential amounting to ∼9 cm(-1).

Far-infrared spectroscopy of syn-vinyl alcohol

Vinyl alcohol has been extensively studied in both the microwavea,b and mid-IRc,d spectral regions, where 9 out of 15 vibrational modes have been identified. Here we present the first far-IR spectrum of vinyl alcohol, collected below 700 cm−1at the Australian Synchrotron. The high resolution (0.001 cm−1) spectrum reveals the ν11 and ν15 fundamentals of syn-vinyl alcohol at 489 cm−1and 407 cm−1, in addition to two hot bands of the ν15 mode at 369 cm−1and 323 cm−1. High J transitions in the R-branch of the ν15 band were found to be perturbed by an a-axis Coriolis interaction with the nearby ν11 state. The ν15 torsional mode of syn-vinyl alcohol was fit using a Watson’s A-reduced Hamiltonian to yield rotational, centrifugal distortion, and Coriolis coupling parameters.