Abstract
The rotational spectra of five isotopic species of the Ar-SiO complex have been observed at high-spectral resolution between 8 and 18 GHz using chirped Fourier transform microwave spectroscopy and a discharge nozzle source; follow-up cavity measurements have extended these measurements to as high as 35 GHz. The spectrum of the normal species is dominated by an intense progression of a-type rotational transitions arising from increasing quanta in the Si-O stretch, in which lines up to v = 12 (~14 500 cm-1) were identified. A structural determination by isotopic substitution and a hyperfine analysis of the Ar-Si17O spectrum both suggest that the complex is a highly fluxional prolate symmetric rotor with a vibrationally averaged structure between T-shaped and collinear in which the oxygen atom lies closer to argon than the silicon atom, much like Ar-CO. To complement the experimental studies, a full dimensional potential and a series of effective vibrationally averaged, two-dimensional potential energy surfaces of Ar + SiO have been computed at the CCSD(T)-F12b/CBS level of theory. The equilibrium structure of Ar-SiO is predicted to be T-shaped with a well depth of 152 cm-1, but the linear geometry is also a minimum, and the potential energy surface has a long, flat channel between 140 and 180°. Because the barrier between the two wells is calculated to be small (of order 5 cm-1) and well below the zero-point energy, the vibrationally averaged wavefunction is delocalized over nearly 100° of angular freedom. For this reason, Ar-SiO should exhibit large amplitude zero-point motion, in which the vibrationally excited states can be viewed as resonances with long lifetimes. Calculations of the rovibrational level pattern agree to within 2% with the transition frequencies of normal and isotopic ground state Ar-SiO, and the putative Ka = ±1 levels for Ar-28SiO, suggesting that the present theoretical treatment well reproduces the salient properties of the intramolecular potential.
Recommended Citation
M. C. McCarthy et al., "The Rotational Spectrum and Potential Energy Surface of the Ar-SiO Complex," Journal of Chemical Physics, vol. 149, no. 13, American Institute of Physics (AIP), Oct 2018.
The definitive version is available at https://doi.org/10.1063/1.5048202
Department(s)
Chemistry
Research Center/Lab(s)
Center for High Performance Computing Research
Keywords and Phrases
Crystal Atomic Structure; Geometry; Ground State; Isotopes; Microwave Spectroscopy; Molecular Physics; Potential Energy; Potential Energy Surfaces; Quantum Chemistry; Rate Constants; Silicon Oxides; Spectral Resolution, Equilibrium Structures; Fourier Transform Microwave Spectroscopy; High Spectral Resolution; Intramolecular Potential; Structural Determination; Theoretical Treatments; Transition Frequencies; Vibrationally Excited State, Silicon Compounds
International Standard Serial Number (ISSN)
0021-9606; 1089-7690
Document Type
Article - Journal
Document Version
Final Version
File Type
text
Language(s)
English
Rights
© 2018 The Authors, All rights reserved.
Publication Date
01 Oct 2018
Comments
The work in Cambridge is supported by NSF Grant Nos. CHE-1058063 and CHE-1566266. R.D. is supported by the US National Science Foundation (No. CHE-1566246).