Michio Matsushita

Electron spin resonance studies of the methane radical cations (12,13CH+4, 12,13CDH+3, 12CD2H+2, 12CD3H+, 12CD+4) in solid neon matrices between 2.5 and 11 K: Analysis of tunneling

The radical cation of methane isolated in neon matrices exhibits highly unusual electron spin resonance (ESR) spectral features between 2.5 and 11 K. The anomaly has been clarified by invoking large amplitude tunneling motions of the hydrogens among several symmetrically equivalent Jahn–Teller distorted structures. The effect of the tunneling motions upon the ESR spectrum was investigated by an analysis scheme based upon permutation–inversion group theory. All the deuterium substituted cations, i.e., CDH+3, CD2H+2, CD3H+, and CD+4 were also studied. The hyperfine coupling constant of 13C was obtained from the study of 13CDH+3 and 13CH+4. Several independent generation methods were employed during the course of these methane cation studies, including photoionization, electron bombardment, x‐irradiation, and a pulsed laser surface ionization technique.

Internal rotation of the methyl group in the radical cation of dimethyl ether

The radical cation of dimethyl ether has been studied by ESR in the temperature region of 6–140 K focusing on the internal rotation of the methyl groups. The methyl groups rotate almost freely at above ∼70 K to give a septet ESR spectrum. At temperatures below 40 K there emerge extra lines due to the tunneling rotation of the methyl groups. From the analysis of the line shape, the interaction potential for the rotation of the two methyl groups, if any, should be approximated as proportional to cos 3θ1 cos 3θ2, where θ1 and θ2 denote the rotational angles of the methyl groups measured from the potential minima of the internal rotation of the methyl groups. The activation energy for the thermally induced internal rotation is determined to be ∼100 cal/mol at temperatures above 25 K, whereas at lower temperatures the apparent activation energy drops sharply, which is consistent with the quantum tunneling of the methyl protons. The small activation energy of 100 cal/mol for the radical cation is compatible wit...

Group theoretical study of the radical cation of methane: The effect of tunneling motions on the hyperfine interaction

The electron spin resonance (ESR) spectrum of CH+4 indicates that some large amplitude tunneling motions among Jahn–Teller distorted structures make the four protons equivalent. A group theoretical study using the permutation–inversion (PI) group is performed to analyze the hyperfine interaction of the nonrigid CH+4. It is shown that three patterns of the interaction are possible depending upon the type of tunneling motions. Only one of the three patterns is consistent with the experimental spectrum, which is presented in the accompanying paper [J. Chem. Phys. 103, 3377 (1995)].

Novel Organic Ions of High-Spin States

Abstract The interrelation between spin alignment and a charged organic molecular field has been investigated. The monoanion (monocation) of m-phenylenbis(phenylmethylene), a ground-state quintet alternant hydrocarbon, was formed at 77 K via the photolysis of the ionized diazo precursor generated via gamma-radiolysis in the frozen solution of 2-methyltetrahydrofu-ran (butyl chloride). Both the ions exhibited similar ESR spectra identified as due to a ground-state quartet with g = 2.003 (2.003), D = +0.1200 (+0.1350, +0.1285) cm−1 and |E|= 0.0045 (0.0040, 0.0055) cm−1 for the anion (cation). The quartet state is consistent with the monoions of the parent quintet molecule with the four singly-occupied orbitals, i.e., the two pi nonbonding molecular orbitals (NBMO) and the two in-plane nonbonding orbitals at the divalent carbon atoms. It was concluded by proton-ENDOR that both the excess electron and the hole occupy one of the two singly occupied pi NBMO, the spins in the in-plane nonbonding orbitals being l...

Molecular motion of the radical cations in the condensed phase as studied by ESR: diazabenzenes

Abstract The radical cation of three diazabenzenes, pyridazine, pyrimidine, and pyrazine, have been investigated by ESR in the temperature region of 6-143 K. The observed spectra changes have been analyzed by the density matrix method with a model of uniaxial rotation of the radicals. A conspicuous difference in the dynamical behavior of the three similar systems is found.

Radical Cations of Aliphatic Ethers

We will focus our subject to aliphatic ethers for the reasons; 1) they are one of the fundamental types of organic molecules and 2) despite their relatively simple composition, radical cations thereof expose many facets interesting enough to basic scientists and educative enough to students who want to deepen their understanding of vividness and subtlety of molecules. To be more specific, the radical cation of dimethylether provides a nice case for studying the internal rotation of the methyl group while the cations of acetals and dioxanes are a suitable system for analyzing the orbital interaction, for example. In the succeeding sections we will deal with several ethers dividing them into sections according to the topic to be emphasized.

The insignificance of the interference of •CFCl2 radical in the electron spin resonance study of radical cations using the CFCl3 matrix

The insignificance of the ‘‘background’’ signal due to the •CFCl2 radical in the ESR study of radical cations using the CFCl3 has been demonstrated by calculating the dipolar broadening of the hyperfine interaction.