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Microwave rotation-tunneling spectroscopy of the water–methanol dimer: Direct structural proof for the strongest bound conformation

Stockman, Paul A. and Blake, Geoffrey A. and Lovas, Frank J. and Suenram, Richard D. (1997) Microwave rotation-tunneling spectroscopy of the water–methanol dimer: Direct structural proof for the strongest bound conformation. Journal of Chemical Physics, 107 (10). pp. 3782-3790. ISSN 0021-9606. doi:10.1063/1.474736.

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Rotation-tunneling a-type spectra of CH3OH[centered ellipsis]H2O and CH3OD[centered ellipsis]D2O were recorded between 18 and 60 GHz using direct absorption microwave spectroscopy, and for CH3OH[centered ellipsis]H2O, 13CH3OH[centered ellipsis]H2O, CH3OH[centered ellipsis]DOH, CD3OH[centered ellipsis]H2O, and CH3OD[centered ellipsis]D2O between 7 and 24 GHz using a Fourier-transform microwave spectrometer. Because CH3OH and H2O are capable of both accepting and donating hydrogen bonds, there exists some question as to which donor–acceptor pairing of the molecules is the lowest energy form. This question is further emphasized by the ambiguity and variety present in previous experimental and computational results. Transitions arising from the methyl torsional A state were assigned in each of the studied isotopomers, and for the A and E states in CH3OH[centered ellipsis]H2O. While the measured components of the dipole moment for the parent (H,12C,16O) isotopomer—µa = 7.956 ± 0.03 × 10^–30 C m (2.385 ± 0.008 D), µb = 3.636 ± 0.02 × 10^–30 C m (1.090 ± 0.006 D), µc = 0.43 ± 0.47 × 10^–30 C m (0.13 ± 0.14 D), where the errors correspond to 1 sigma uncertainties—are consistent with either conformation, the fit of the structure to the rotational constants demonstrates unambiguously that the lower-energy conformation formed in supersonically cooled molecular beams corresponds to a water–donor, methanol–acceptor complex. The results and implications for future work are also discussed in terms of the permutation-inversion theory presented by Hougen and Ohashi [J. Mol. Spectros. 159, 363 (1993)].

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Blake, Geoffrey A.0000-0003-0787-1610
Additional Information:© 1997 American Institute of Physics (Received 24 March 1997; accepted 9 June 1997) This research was supported in part by a grant from the National Science Foundation (CHEM-9415488). We thank J. T. Hougen and N. Ohashi for discussions about their work on the permutation-inversion theory of the water–methanol dimer.
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Subject Keywords:organic compounds; water; microwave spectra; rotational states; tunnelling spectra; molecular configurations; hydrogen bonds; molecular moments; quasimolecules; Fourier transform spectra
Issue or Number:10
Record Number:CaltechAUTHORS:STOjcp97
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ID Code:2247
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Deposited On:19 Mar 2006
Last Modified:08 Nov 2021 19:46

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