Study of Potential Interstellar Molecules: Nuclear Quadrupole Coupling Constants of the Nitrogen Atom in Pyrrole

Abstract

The nuclear quadrupole coupling constants of the nitrogen atom in pyrrole have been redetermined by analysis of the hyperfine structure for several low J rotational transitions. The resulting values arex"" = 1'400±O'OO8 MHz and Xbb = 1·300±O·OO8 MHz. Small modifications to the previously reported rotational constants are given.Recent interest in the discovery of molecules in interstellar space led us to investigate the possibility of finding pyrrole, a simple heterocyclic compound containing atoms of only carbon, hydrogen and nitrogen. The importance of pyrrole in relation to the exobiology of porphyrins has recently been emphasized and a plea made for a search in the region of Sagittarius (Hodgson 1971). As a preliminary to the interstellar search, it was necessary to study several low J absorptions ofpyrrole in the laboratory. The microwave spectrum, including the nitrogen quadrupole analysis,was published by Nygaard et al. (1969) but during our study of the Ill-ItO transition it became evident that the multiplet structure of the absorption could not be accurately predicted using the published microwave data. We therefore decided to study several multiplets of pyrrole in order to obtain more accurate values of the nitrogen quadrupole coupling constants.Pyrrole (Koch-Light. pure grade) was used without further purification. Spectra were recorded using a conventional 5 kHz Stark-modulated G band spectrometer. Frequency measurements were made with a Hewlett-Packard 5246L electronic counter which was calibrated periodically against a Sulzer 2· 5C laboratory standard. Absolute frequencies of hyperfine components are quoted to an accuracy of ± 10kHz whereas frequency differences, between various components of the multiplet, can be determined to within ± 5 kHz. The pyrrole sample was contained in a dry-ice cooled absorption cell at pressures of approximately 1 J.tmHg (0'13 Pa). Time constants of the orders of 1 s were used whilst scanning the multipiets.A maximum resolution of 20 kHz half-width was achieved for the l 1C 1 10 transition. Substitution of the frequency separation between successive members of this multiplet into the well-known relationship of Casimir (1936)

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

“…This suggests that the electric field gradient around the N nuclei is similar in the complex than in the isolated pyrrole. 37 Similar values of the quadrupole constants have been also found for the Pyr-Ar complex 20 (Table 6). The quadrupole constants of Pyr-Ne present slightly larger deviations from the monomer values, probably due to the fact that the b (or c) axis does not lie in the ring plane.…”

“…2. On first inspection the broadband rotational spectrum is dense with lines corresponding to several species previously identified, including pyrrole monomer 36,37 and its 13 C and 15 N isotopic species, 38 pyrrole dimer, 19 and pyrrole-water complexes. 39 After removing the known lines from the spectrum, two strong c-type lines consistent with the 14 N nuclear quadrupole hyperfine pattern expected for the 1 10 ' 0 00 transitions were firstly assigned to the Pyr- 20 Ne and Pyr- 22 Ne species.…”

Gas-phase tautomeric equilibrium of 2-pyridinone and 2-hydroxypyridine by microwave spectroscopy

“…In the present study, we have used a conventional Starkmodulated spectrometer in the range [28][29][30][31][32][33][34][35][36][37][38][39][40] GHz and a jet-cooled millimeter-wave spectrometer28 in the range 48-72 GHz to measure the spectra of 2-hydroxypyridine and 2-pyridinone. By considering line intensities and then accounting for dipole moments and the vibrational partition functions, the respective concentrations of the species have been determined.…”

Effects of Chlorination on the Tautomeric Equilibrium of 2‐Hydroxypyridine: Experiment and Theory

“…À2.876 (7) [41] À2.700(1)1.406 (1) For the sake of clarity,F igure 4s hows the shifts of the relative energies of each tautomer upon chlorination, for which the reference value (fixed to zero) is the calculated energy differenceb etween the OH s and the C=Ot automers for the 2HP species( DE 0 2HP ). From Figure 4, we can easily deduce that the shifts of the relative energies upon chlorinationo ft he tautomers are consistent fort he two methods( MP2 and B3LYP).…”