John Sheridan

The rotational and vibrational spectra, structure and dipole moment of 1,3-dioxole-2-thione

Abstract Rotational and centrifugal distortion constants are determined for the ground state and several excited states of the lowest vibrational mode of l,3-dioxole-2-thione, the “envelope” ring-bending mode. The structure of the molecule is planar. The A-constant is 1% larger than that of 1,3-dioxole-2-one (vinylene carbonate), which indicates small changes in ring-geometry on substituting Cue5fbS for Cue5fbO. The dipole moment of 1,3-dioxole-2-thione deduced from Stark-effect measurements is (1.60 ± 0.02) × 10 −29 Cm (4.81 ± 0.06 D). IR and Raman spectra lead to a complete analysis of the normal modes of vibration, based partially on a normal coordinate calculation.

The rotational and vibrational spectra of 1,3-dithiole- 2-one

Abstract Microwave spectra of 1,3-dithiole-2-one show that the molecule has a planar equilibrium conformation. IR and Raman spectra are analysed to give the normal modes of vibration.

Microwave Spectrum of Chloroacetylene in Ground and Excited Vibrational States

The microwave spectrum of chloroacetylene in the ground and excited states has been investigated in the frequency range 15 to 306 GHz. Ground state rotational and nuclear quadrupole coupling constants for twelve isotopic species of chloroacetylene and accurate distortion constants were determined for two of these. The data allowed the rs-structure of chloroacetylene to be reconsidered and the internal consistency of this method of structure determination to be checked. Rotational spectra in five vibrationally excited states, with energy up to 700 cm-1 were observed for four different isotopic species and spectroscopic constants for these states were derived.

The Micro wave Spectrum of Bromoacetylene ; rs-Structure , Dipole Moment, Quadrupole Coupling Constants and Excited Vibration States

Abstract The microwave spectrum of bromoacetylene has been investigated in the frequency range from 7 GHz to 35 GHz. From Stark effect measurements the dipole moment has been determined as μ = 0.23 + 0.01 D, and the restructure has been derived in four independent ways from twelve isotopic species: C - H = 1.0553 Å, C ≡ C = 1.2038 Å, C - Br = 1.7913 Å (internal consistency better than ± 0.0003 Å). Quadrupole coupling constants have been determined for eleven isotopic forms and are e q Q = 541.47 MHz and 648.00 MHz for HCCBr81 and HCCBr79, respectively. Rotation spectra have also been observed for excited states of the three lowest normal modes and for several isotopic forms. For the Br81 (Br79) species the rotation-vibration coefficients are α5 = -10.98 (-11.02) MHz, α4 = -1.57 (- 1.61) MHz and α3 = + 12.88 (+ 13.40) MHz. For the bending vibrations, ν5 and ν4 , l-type doubling constants are obtained as ql5 = 4.14 (4.17) MHz and ql4 = 2.6 MHz. Analysis of the Fermi resonance between the first excited state of ν3 and the l = 0 component of the second excited state of ν5 gives the mixing ratio of these two states as a/b = 1.45 (1.51) and the interaction energy as W3,5 = 1.313 (1.181) δ3,5 for the Br81 (Br79) species. With an approximate value of δ3,5 ≌ 25 cm-1, the cubic force constant is obtained as κ3,55 ≌ 44 cm-1. The results are discussed in relation to the molecular properties of other halogen acetylenes and halogen cyanides.

Internal rotation and 14N quadrupole coupling of 3- and 5-methylisoxazole

Abstract In the following we present a 14 N quadrupole hyperfine structure, a fourth-order centrifugal distortion, and an IAM methyl internal rotation analysis of 3- and 5-methylisoxazole. The measurements were done in the frequency range of 8 to 26 GHz employing a microwave Fourier transform spectrometer.

Walter Gordy: some memories and impressions

With the death of Walter Gordy it was clear to many physicists and chemists, and especially to those who knew him as a person, that the world of radiospectroscopy and molecular physics had lost one of its more versatile and colourful characters. For something like thirty years he was the dominant figure in the quest for scientifically usable radio waves at the shortest possible wavelengths, an objective which he pursued with dramatic success and with relentless energy. For a more complete picture of the man, however, we must also look into the ways in which this energy was also directed into various other areas of physics and chemistry. A scientist’s first research, and how he or she describes it, can often give keys to the person’s general approach to scientific problems, and indeed can often show a pattern of interests to be sustained over a long period. This applies in some degree to Gordy, but an examination of his early work leaves us aware, not for the only time, that generalizations such as that above do not apply well to him. Beginning in 1934 and continuing through the remainder of that decade, Gordy’s early publications were of infra-red spectroscopic studies of liquids and solutions. The early work was associated with the names of E.K. Plyler and Dudley Williams, at the Physics Department of the University of North Carolina, and continued in the later part of this period when Gordy was at the Mary Hardin-Baylor College in Belton, Texas. Perhaps it was during this time that he, a Southerner by birth and to some extent by temperament, became what he once described to me as “a Texas fan”. The frontier spirit of that state no doubt suited his approach to science and to life. In some thirty papers up to 1941, Gordy’s work shows a strong awareness of chemical bonding and structure. Mostly this was in relation to molecular interactions in liquids, particularly hydrogen bonding, spectroscopic studies of which were becoming recognized [ 11 as a very direct means to new clear-cut

The Microwave Spectrum of 4-Methylisoxazole: 14N Nuclear Quadrupole Coupling, Methyl Internal Rotation and Electric Dipole Moment

The microwave spectrum of 4-methylisoxazole has been investigated in the frequency range from 8 to 40 GHz, employing both Stark and Fourier transform spectroscopy. We present the results from a 14N quadrupole hyperfine structure, a fourth-order centrifugal distortion and an IAM methyl internal rotation analysis. The components of the electric dipole moment with respect to the principal axes of inertia have been obtained from the Stark splittings of some rotational lines.

14N Nuclear Quadrupole Coupling and Methyl Internal Rotation of 2-, 4-, and 5-Methyl Oxazole

In the following we give an outline of 14N nuclear quadrupole, internal axis method (IAM) methyl internal rotation, and fourth order centrifugal distortion - only needed for extrapolating transition frequencies to higher J values - analyses performed for 2-, 4-, and 5-methyl oxazole. The results are discussed, the three methyl oxazoles being compared with one another and with their common parent, oxazole.

The rotational spectra of fluorinated acetonitriles; 14N-nuclear quadrupole hyperfine structures measured with a microwave Fourier transform spectrometer

Abstract The microwave spectra of CF3CN, CH2FCN, CHDFCN, CD2FCN and CHF2CN have been measured and analysed. The nuclear quadrupole hyperfine splittings due to 14N have been measured by Microwave Fourier Transform spectroscopy. The nuclear quadrupole coupling constants, transformed to the bonding axis systems of the C-C ≡ N groups, are shown to be in accord with structural predictions of the p-electron populations at the nitrogen atom.

The Microwave Spectrum of Oxazole

The dipole moments and the quadrupole coupling constants of the normal and the three mono-deuterated species of oxazole have been measured. The dipole moment of 1.50 ± 0.03 D is found to deviate by 10.8° from the external bisector of the CNC angle towards the C(2) carbon atom. The principal values of the quadrupole coupling tensor are determined as Xzz = -4.04 ± 0.02 MHz and Xxx - 1-66 ± 0.02 MHz along the axes in the molecular plane, so that the gradient perpendicular to this plane is Xyy = 2.38 MHz. The direction of the largest gradient deviates by 5.7° from the external bisector of the CNC angle towards the carbon atom C(4). An attempt is made to correlate these results and the geometry of oxazole with the electron distribution in this molecule