The rotational spectrum and potential energy surface of the Ar–SiO complex

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...

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Veröffentlicht in:The Journal of chemical physics 2018-10, Vol.149 (13), p.134308-134308
Hauptverfasser: McCarthy, Michael C., Ndengué, Steve Alexandre, Dawes, Richard
Format: Artikel
Sprache:eng
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Zusammenfassung: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.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.5048202