title: Geometry of an Isolated Dimer of Imidazole Characterised by Rotational Spectroscopy and Ab Initio Calculations.
abstract: An isolated, gas-phase dimer of imidazole is generated through laser vaporisation of a solid rod containing a 1:1 mixture of imidazole and copper in the presence of an argon buffer gas undergoing supersonic expansion. The complex is characterised through broadband rotational spectroscopy and is shown to have a twisted, hydrogen-bonded geometry. Calculations at the CCSD(T)(F12*)/cc-pVDZ-F12 level of theory confirm this to be the lowest-energy conformer of the imidazole dimer. The distance between the respective centres of mass of the imidazole monomer subunits is determined to be 5.2751(1) Å, and the twist angle γ describing rotation of one monomer with respect to the other about a line connecting the centres of mass of the monomers is determined to be 87.9(4)°. Four out of six intermolecular parameters in the model geometry are precisely determined from the experimental rotational constants and are consistent with results calculated ab initio.
authors.affiliation: School of Chemistry, Bedson Building, Newcastle University, Newcastle upon Tyne, Tyne and Wear, NE1 7RU, UK.
authors.forename: John C
authors.identifier: http://orcid.org/0000-0002-1186-6091
authors.initials: JC
authors.lastname: Mullaney
authors.affiliation: School of Chemistry, Bedson Building, Newcastle University, Newcastle upon Tyne, Tyne and Wear, NE1 7RU, UK.|Argonne National Laboratory, Chemical Sciences & Engineering, 9700 S. Cass Ave., Bldg. 200, Lemont, IL, 60439, USA.
authors.forename: Daniel P
authors.identifier: http://orcid.org/0000-0003-0153-9158
authors.initials: DP
authors.lastname: Zaleski
authors.affiliation: School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK.
authors.forename: David P
authors.identifier: http://orcid.org/0000-0002-3220-4177
authors.initials: DP
authors.lastname: Tew
authors.affiliation: School of Chemistry, Bedson Building, Newcastle University, Newcastle upon Tyne, Tyne and Wear, NE1 7RU, UK. nick.walker@newcastle.ac.uk.
authors.forename: Nicholas R
authors.identifier: http://orcid.org/0000-0002-9450-305X
authors.initials: NR
authors.lastname: Walker
authors.affiliation: School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK. a.c.legon@bristol.ac.uk.
authors.forename: Anthony C
authors.identifier: http://orcid.org/0000-0003-3468-9865
authors.initials: AC
authors.lastname: Legon
keywords: ab initio calculations; dimerization; hydrogen bonds; nitrogen heterocycles; rotational spectroscopy