Alan Carrington

Infrared predissociation spectrum of the H+3 ion

We have observed an infrared spectrum of the H+3 ion containing nearly 27 000 lines which span only 222 cm−1 from 872 to 1094 cm−1. A beam of H+3 ions at a potential of from 1.2 to 10.5 kV is aligned to be collinear with an infrared laser beam from a carbon dioxide cw laser. Photodissociation occurs to produce fragment H+ ions which are separated from the parent H+3 ions using an electrostatic analyzer. Doppler tuning is accomplished by scanning the H+3 ion beam potential and resonance lines corresponding to an increase in fragment H+ ion current are detected by means of a velocity modulation technique. The observed linewidths range from 3 to 60 MHz, with additional broader lines also being detected by chopping the laser beam. We believe that each resonance line arises from predissociation of H+3 to form H2 and H+. Pseudo‐low resolution spectra constructed by computer convolution of the experimental data show well defined peaks which correspond closely in transition frequency to j=3–5 rotational transitio...

Electron spin resonance spectra of nitrogen heterocyclic radical ions

The e.s.r. spectra of the negative ions of a variety of nitrogen heterocyclic molecules have been measured and the proton and nitrogen hyperfine coupling constants determined. The proton splittings are interpreted using Huckel-type molecular orbital calculations with an adjustable Coulomb parameter for the nitrogen atom. The results indicate that the nitrogen splitting is proportional to the unpaired electron density on the nitrogen atom, the proportionality constant QN having the value 25 ± 2 gauss. No significant dependence of the nitrogen splitting on the spin density on adjacent carbon atoms is observed.

Electron spin resonance studies of hyperconjugation in aromatic ions

We have found strong evidence that the main interaction between methyl groups and the ring system in the positive ions of aromatic hydrocarbons involves hyperconjugation rather than an inductive effect. The methyl proton hyperfine splittings have been compared in the e.s.r. spectra of both positive and negative ions of 9-methylanthracene and 9,10-dimethylanthracene. The splittings are about twice as large in the positive ions, which is expected if hyperconjugation takes place, but cannot be explained by an inductive model. The ring proton splittings have also been measured, and show small variations which can be explained satisfactorily by either theory.

The electron spin resonance spectrum and spin density distribution of the benzyl radical

The benzyl radical has been generated in aqueous solution by means of a continuous flow system. The electron spin resonance spectrum is almost completely resolved, and accurate values for the four proton hyperfine splittings are obtained. The spin density distribution in the benzyl radical is calculated by various methods and the relationship between theoretical spin densities and proton hyperfine constants is studied.

Electron spin resonance line widths of transition metal ions in solution. Relaxation through zero-field splitting

The factors which determine the electron resonance line widths of transition metal complexes in solution are considered. For complex ions possessing two or more unpaired electrons the dominant relaxation mechanism arises from coupling of the zero-field splitting of the spin multiplet with the random tumbling of the molecules in fluid solution. The theory of this effect is re-examined using the time-dependent density matrix methods of Redfield.

Spectroscopy of the hydrogen molecular ion

The theory and spectroscopy of the hydrogen molecular ion in its isotopic forms H2+, HD+ and D2+ is reviewed. Theoretical treatments are directed towards the calculation of potential energy curves, vibration-rotation energies and nuclear hyperfine constants. In the Born-Oppenheimer approximation the Schrodinger equation for H2+ can be solved exactly, but further approximations must be developed to describe the coupling of electronic and nuclear motion. The lack of a centre of symmetry in HD+ creates difficulties in the theory. Radiofrequency hyperfine transitions have been measured for H2+ using quadrupole trapping and photoalignment. Ion beam methods have been used to measure vibration-rotation transitions in HD+, and attention has been paid to levels very close to the dissociation limit. Analysis of proton and deuteron nuclear hyperfine structure reveals extreme asymmetry of the electron distribution in these levels. The hyperfine interactions have been measured by radiofrequency/infrared and microwave/infrared double resonance experiments. An electronic spectrum of D2+ arising through excitation from the ground electronic state to the excited long-range state has been measured using both infrared and microwave radiation. Observation of a microwave electronic transition in H2+ has provided experimental identification of the related H;H long-range complex.

Gas‐Phase Electron Resonance Spectrum of ClO

The electron resonance spectrum of ClO in the gas phase is described, and the theoretical analysis is discussed in detail. As a result of this analysis, values of the following molecular constants are obtained. The fine‐structure constant A = − 282±9 cm−1, the rotational constant B0=0.622±0.001 cm−1 (for 35Cl16O), the 35Cl nuclear hyperfine constant h = 111±2 Mc/sec, and the 35Cl quadrupole coupling constant e2Qq=−88±6 Mc/sec. Corresponding values of the 37Cl hyperfine constants are also obtained. The results are discussed in terms of the expected ground‐state electron configuration of the radical.

Electric dipole moments of open-shell diatomic molecules

The electric dipole moments of the diatomic radicals IO, SF, SeF and SeO (1Δ) have been determined by studying the Stark splitting in their gas phase electron resonance spectra. Previous measurements for several other diatomic radicals are repeated and, in particular, earlier results for NS and SO (1Δ) are corrected.

The electron spin resonance spectra of the toluene, p-xylene and m-xylene anions

The electron spin resonance (e.s.r.) spectra of the anions of toluene, p-xylene and m-xylene have been studied and the proton hyperfine coupling constants determined. These are in excellent agreement with the predictions of Huckel molecular orbital theory.

Electron resonance studies of the renner effect

The gas phase electron resonance spectra of NCO in its ground 2Π3/2 vibronic state and in two excited vibronic states are described. Theoretical analysis of the spectra yields effective g values for the three states. In additon the 14N magnetic hyperfine and electric quadrupole coupling constants and the electric dipole moment are determined. The theory of the Renner coupling of electronic and vibrational motion is extended, and shown to account for anomalous contributions to the g values. The theory also shows that these contributions are closely related to the Renner coupling constant.