Pyrrole-argon: microwave spectrum, structure, dipole moment, and nitrogen-14 quadrupole coupling constants

Abstract

The rotational spectrum of the weak complex between argon and pyrrole has been observed by use of a Fourier transform microwave spectrometer with a pulsed supersonic nozzle molecular beam source. The complex is a nearly symmetric prolate top with the Ar atom located above the plane of pyrrole, 3.553 (10) A from the pyrrole center of mass. The line between the Ar atom and the pyrrole center of mass makes an angle of 5 . 5 (20)' with the normal to the pyrrole plane and is displaced toward the N atom. The dipole moment of the complex, 1.707 (3) D, is smaller than that of free pyrrole, 1.767 (2) D, and the negative end of the complex's dipole moment is rotated from the pyrrole plane toward the Ar atom. The I4N quadrupole coupling constants have been determined. Based on the centrifugal distortion constant 0, and a pseudcdiatomic model, the binding energy of the complex is estimated to be 300 cm-I. The dipole moment and I4N quadrupole coupling constants of pyrrole were redetermined.The laser-induced fluorescence (LIF) spectra of trans-stilbene in a supersonic free jet have been investigated to discuss the vibrational level structure in the SI state. Since the rotational temperature is reduced to as low as 1.5 K, the congested vibronic bands can be resolved to uncover the level structure in the SI state. The rotational band contours have been measured to determine structural parameters of the SI state. It is concluded that in the SI state the C=C bond length, r c e , is larger by 0.05 A and the C=C-C angle, t9c,c--c, is smaller by 10' than those in the So state. Most of the transition lines to the SI vibrational levels above 800 cm-' exhibit splittings caused by Fermi coupling. The number of the observed split bands is larger in a transition to a higher Si vibrational level. Above 1200 cm-' from the band origin, the line broadening is found for respective lines, and this is attributed to a congestion caused by Fermi coupling with dense background levels. The observed change in the level structure caused by 13C or D isotope substitution is ascribed to differences between the level coupling schemes in the normal and isotopic species.

Tautomerism and Microsolvation in 2-Hydroxypyridine/2-Pyridone

“…For pyrrolic nitrogens cc is negative. 16,39,40 In contrast, pyridinic nitrogens have positive values of cc . 16,40,41 The experimental values of -2.18 and 1.993 MHz in Table 1 allow us to establish unambiguously the presence of the keto and enol tautomers, respectively, and the conclusive identification of the 2PO-H 2 O and 2HP-H 2 O monohydrates in our supersonic expansion.…”

Rotational spectrum, structure and internal dynamics of the pyrrole·ammonia complex

“…As far as pyrrole containing dimers are concerned, only few microwave investigations of their rotational spectra have performed so far, namely the pyrrole dimer [11], the pyrrole.argon [12] and the pyrrole.water complex [13]. With our study on pyrroleÁammonia, not only information on the complex structure and dynamics, but also about the electronic charge distribution around the N-nucleus at both moieties is obtained.…”

Chemistry at Low Pressure and Low Temperature: Rotational Spectrum and Dynamics of Pyrimidine-Neon

“…Let us consider, for the sake of simplicity, only complexes with aromatic unsubstituted rings. Only adducts with Ar have been studied with MBMWFT for the three prototype five-membered aromatic compounds, furan (furanAr [11] was the first observed adduct of a rare gas with a cyclic molecule), pyrrole, [12] and thiophene, [13] and for some other five-membered molecules with two heteroatoms.…”