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.

Strained hydrogen bonding in imidazole trimer: a combined infrared, Raman, and theory study

“…The level of computation chosen to conduct the bulk of the calculations (B3LYP-D3(BJ)/ def2-TZVP) seems to be at least adequate for the structure optimizations. This is analyzed in Table 1 by comparison to experiment for the monomer 50 and the dimer 16 in two different ways. One is to allow for an up to E1% decrease in the rotational constants upon vibrational averaging.…”

“…In the Table S1 of ref. 16, a CCSD(T)-F12C/cc-pVDZ-F12 structure is presented (although from the text in the article, it is not completely unambiguous whether it is a full CCSD(T) optimization). Its three equilibrium rotational constants uniformly deviate from experiment by 0.5%.…”

“…This dimer has been characterized vibrationally in helium droplets 14,15 and rotationally in the gas phase, using microwave spectroscopy. 16 Argon matrix isolation was less conclusive, and what was denoted as a dimer signal 1 around 3000 cm À1 is more likely due to large clusters. The imidazole trimer as the first cluster size capable of forming a concerted hydrogen bond cycle has been postulated and calculated before, 17 but its vibrational spectrum in the gas phase has remained unassigned.…”

Conformational isomers oftrans-urocanic acid observed by rotational spectroscopy

“…[39][40][41] A tendency for the described experimental conditions to generate products of the fragmentation of precursors has been noted during recent studies of imidazole and pyrazole derivatives. 18,42,43 Godfrey et al…”

An Innovative Approach for the Generation of Species of the Interstellar Medium

“…These experimental approaches have also been applied successfully to many other relevant building blocks of life, [32][33][34][35][36] synthesizing metal-containing species [37][38][39][40] and molecular complexes. [41][42][43][44] Significant photo-fragmentation effects were revealed; unwanted lines of decomposition products appeared in crowded rotational spectra. Consequently, we improved our laser ablation experiments to minimize the photo-fragmentation.…”