Rotational spectrum and molecular properties of pyridine⋯xenon

Rotational Spectra of 2-Ethynylpyridine and Its Monohydrate: Influence of the Ortho-Substitution on Ring Geometry and Intermolecular Hydrogen Bonds

Rotational spectra of the 2-ethynylpyridine monomer and its monohydrate have been characterized by pulsed jet Fourier transform microwave spectroscopy complemented with quantum chemical calculations. The measurements of rotational transitions of the 2-ethynylpyridine monomer and its eight monosubstituted isotopologues (¹⁵N and ¹³C) in natural abundances allow an accurate structural description of the skeleton of 2-ethynylpyridine. For the monohydrate, only the most stable isomer, stabilized by an O-H···N and a secondary C-H···O hydrogen bonds, has been observed in the supersonic jet. Johnson's noncovalent interaction and quantum theory of atoms in molecules analyses have been performed and compared with results for several ortho-substituted pyridine derivatives to elucidate the general trend in their binding energies.

CRASY: correlated rotational alignment spectroscopy of pyridine. The rotational Raman spectrum of pyridine and asymmetric fragmentation of pyridine dimer cations

We investigated the rotational Raman spectrum of pyridine monomers and pyridine dimers with mass-correlated rotational alignment spectroscopy (mass-CRASY) and ab initio calculations. The mass spectrum showed a strong signal for the protonated pyridine cation, which we assigned to asymmetric fragmentation of the dimer: ab initio calculations revealed facile proton transfer in the dimer cation and thermodynamically favorable asymmetric fragmentation. In the rotational spectrum correlated to the monomer mass channel, we assigned up to 40 lines for rotational states J ≤ 8. No spectrum could be assigned for the dimer, possibly due to the theoretically predicted presence of multiple dimer structures.

Rotational spectra of van der Waals complexes: pyrrole-Ne and pyrrole-Ne2

The van der Waals 1 : 1 and 1 : 2 adducts between the aromatic molecule pyrrole (Pyr) and the rare gas atom neon (Ne) have been investigated using a combination of chirped pulse Fourier transform microwave spectroscopy and quantum-chemical calculations. Rotational spectra of two and three isotopologues of Pyr-Ne and Pyr-Ne2, respectively, arising from the combinations of the 20Ne and 22Ne isotopes, were identified and a partial rs structure determined. Unusual spectral intensities have been observed with a significant enrichment of heavier isotopic species in the jet molecular expansion. The observed rotational constants of Pyr-Ne are consistent with a nearly symmetric prolate top with the Ne atom located above the plane of pyrrole. The trimer presents C2v symmetry with the Ne atoms located one on each side of the ring plane. The experimental 14N nuclear quadrupole coupling constants have been determined for all the isotopologues of Pyr-Ne and Pyr-Ne2 complexes. Similar values to those of isolated pyrrole have been found, which suggests that the electrical gradient field of pyrrole does not change much upon complexation. The observed spectroscopic parameters have been compared with those of other aromatic-rare gas complexes.

Rotational study on the van der Waals complex 1-chloro-1,1-difluoroethane-argon

The rotational spectrum of the van der Waals complex formed between 1-chloro-1,1-difluoroethane and argon has been investigated by using a pulsed jet Fourier transform microwave spectrometer. Only one set of rotational transitions belonging to the lowest energy conformer has been observed and assigned, although theoretical calculations suggest six stable conformers that might be observed. The observed conformer, according to the experimental evidence from two isotopologues (³⁵Cl and ³⁷Cl), adopts a configuration in which the argon atom is located, close to the CF₂Cl top, between the CCF and CCCl planes (the dihedral angle ∠ArCCCl is 65.2°). The distance between argon atom and the center of mass of CH₃CF₂Cl is 3.949(2) Å. The dissociation energy, with pseudo diatomic approximation, is evaluated to be 2.4kJmol^-1.

Theoretical Study of the Pyridine-Helium van der Waals Complexes

In this study we evaluate a high-level ab initio ground-state intermolecular potential-energy surface for the pyridine-He van der Waals complex, using the CCSD(T) method and Dunning's augmented correlation consistent polarized valence double-ζ basis set extended with a set of 3s3p2d1f1g midbond functions. The potential is characterized by two symmetric global minima of -93.2 cm(-1) that correspond to geometries where the distance between the helium atom and the pyridine center of mass is 3.105 Å and the angle with respect to the pyridine c rotational axis is 3.9°. Six local minima can be observed for geometries with the helium atom in the plane cotaining the pyridine molecule. To further analyze the nature of the intermolecular interactions in the complex, we use symmetry-adapted perturbation theory (SAPT). Additional consideration of the pyridine-He2 complex provides a better insight into many-body nonadditive contributions to intermolecular interactions in systems with more helium atoms.

Interactions between alkanes and aromatic molecules: a rotational study of pyridine-methane

The rotational spectrum of the adduct pyridine-methane shows that methane links to an aromatic molecule apparently through a C-H···π weak hydrogen bond. The shape and the internal dynamics behaviour of this complex are very similar to that of the van der Waals complexes involving aromatic molecules with rare gases.

Microwave spectrum of [1,1]-pyridine-Ne2

We investigated the rotational spectra of six isotopologues of pyridine--Ne(2), formed by combinations of two isotopes of the nitrogen atom ((14)N and (15)N) in pyridine with two isotopes of the rare gas atoms ((20)Ne and (22)Ne), by using pulsed jet Fourier transform microwave spectroscopy. We detected the C(2v) symmetry conformer, denoted as [1,1], where the Ne atoms are located one on each side of the ring plane. The [2,0] species, with the two Ne atoms on the same side of the ring, was not observed. Two structural parameters, R and theta, that localize the rare gas atoms with respect to pyridine have been determined. The (14)N nuclear quadrupole coupling constants have been obtained for the isotopologues containing this nucleus.