J.R. Morton

The optical and electron resonance spectra of SO3

The ionic radical SO3 - has been identified in γ-irradiated single crystals of sodium dithionate, sulphamic acid, potassium sulphamate, potassium amine disulphonate and potassium methane disulphonate. The electron resonance spectrum is a single line with an isotropic g factor of 2·004. The principal values of the 33S hyperfine coupling tensor are 428, 314 and 316 Mc/s, from which the percentages of 3s and 3p character of the unpaired electron orbital are obtained, enabling a value of 111° for the O-S-O angle to be deduced. Ultra-violet transitions at 2700 a and 2400 a were found for SO3 -. A value of 104 for the extinction coefficient of the 2400 a band was measured. A comparison of spin populations between the isoelectronic species PO3 =, SO3 - and ClO3 is included.

The electron spin resonance spectrum of CH3ĊHCOOH at 77°K in l-α-alanine

The change in the electron resonance spectrum of a γ-irradiated single crystal of l-α-alanine on cooling to 77°k has been interpreted in terms of the cessation of rotation of the methyl group of the trapped radical, CH3ĊHCOOH. The isotropic hyperfine couplings of the three hydrogens of the methyl group are found to be 120, 76 and 14 Mc/s respectively compared to the value of 70 Mc/s each at 300°k. The geometry of the free radical at 77°k is such that, in projection on a plane perpendicular to the Ċ-CH3 bond, one of the C-H bonds makes an angle of about 12° to the plane of the free radical centre and this hydrogen is probably adjacent to the carboxyl group.

Electron spin resonance and structure of the ionic radical, ·PO3 =

It is shown that the ionic radical, ·PO3 =, is formed by the action of γ-rays on disodium ortho-phosphite pentahydrate. The hyperfine coupling to the 31P nucleus has principal values of 1967, 1514 and 1513 Mc/s and is consistent with a pyramidal ion having OPO angles of 110°.

The structure, electron resonance and optical spectra of trapped CO3 - and NO3

Examination of irradiated potassium bicarbonate shows the crystal to contain trapped CO3 - radicals, as well as CO2(H) radicals, and examination of irradiated urea nitrate shows this crystal to hold trapped NO3 radicals. Electron resonance spectra and optical absorption spectra suggest that the radicals CO3 - and NO3 are planar, but do not possess a threefold axis. An examination of the expected wavefunction and energies discloses features which favour distortion of these radicals; these features are absent for CO3 = and NO3 -.

The electron spin resonance spectrum of CH3ĊH(CO2H) between 100°K and 200°K

The electron spin resonance spectra of CH3ĊH(CO2H) in γ-irradiated α-alanine between 100°k and 200°k differ from the spectra obtained above and below this range. The ‘intermediate temperature’ spectra are interpreted in terms of a rather critical rate of rotation of the methyl group. From the line-width change near 100°k and 200°k an estimate of approximately 4 kcals has been made for the activation energy hindering the rotation of the methyl group.

Electron spin resonance of γ-irradiated malonic acid

The electron spin resonance spectrum of a γ-irradiated single crystal of malonic acid indicates the presence of at least two chemically distinct radicals. The most stable radical is ĊH(CO2H)2, but the present paper primarily concerns the structure and orientation of the radical ĊH2(CO2H). The anisotropy of the spectra of this radical with respect to the direction of the main magnetic field H shows that the free radical carbon atom has gone over to planar sp 2 hybridization, the HĊH angle being 116°±5°. Since the two ends of the undamaged malonic acid molecule are distinguishable in the crystal, two sites were expected for the radical ĊH2(CO2H). It appears, however, that approximately 80 per cent of the radicals occupy one site, and only about 20 per cent the other. Comparison of the orientation of the main ĊH2(CO2H) radical with that of the undamaged molecule indicates that in the radical the plane of the ĊH2 group is approximately perpendicular to the plane of the (CO2H) group. The spectra of the less pr...

The electron spin resonance spectra of CH(SO3)2 = and N(SO3)2 =

The electron spin resonance spectra of the radical CH(SO3)2 = trapped in a single crystal of potassium methane disulphonate and of the isoelectronic radical N(SO3)2 = in the isostructural potassium amine disulphonate crystal are interpreted. The hyperfine couplings for H, 13C and 14N nuclei and the g-factors are given. The unpaired electron occupies a π-orbital of predominantly central-atom 2p character in each case. The spin populations are derived. An unusual feature, prominent in the potassium methane disulphonate case, is the detection of resolved hyperfine coupling to hydrogen nuclei in the host molecules.

The E.S.R. spectrum of irradiated ammonium hypophosphite

Electron spin resonance spectra of irradiated crystals of ammonium hypophosphite (NH4)+(H2PO2)- indicate that the ionic radical H[Pdot]O2 - is initially formed. The hyperfine interaction tensor of the phosphorus nucleus has the principal values 1698, 1228 and 1228 Mc/s. Interaction with the proton gives rise to an almost isotropic hyperfine coupling of 230 Mc/s. These results indicate that the species H[Pdot]O2 - is irregular tetrahedral in shape, the unpaired electron occupying a hybrid σ orbital centred on the phosphorus nucleus. There is evidence that the radical H[Pdot]O2 - reacts with an adjacent H2PO2 - ion forming the species O2[Pdot]-PHO2 =. The principal values of the hyperfine interaction tensors of the two phosphorus nuclei are 1365, 944, 921 Mc/s and 527, 362, 359 Mc/s respectively. The proton has an isotropic hyperfine coupling of 90 Mc/s. The spectra of irradiated deuterated crystals confirmed this analysis.

Electron spin resonance of (CO2H)CH2CH2ĊH(CO2H) in irradiated glutaric acid

It is concluded from electron spin resonance spectra that the radical (CO2H)CH2ĊH2CH(CO2H) remains trapped in a glutaric acid crystal after γ-irradiation. This radical is found in two different conformations. Approximate hyperfine coupling constants are given for each, although exact interpretation is hindered by the overlapping of spectra. Reasons for the formation of the two forms of the radical are discussed.

Electron spin resonance of γ-irradiated adipic acid

The radical (CO2H)ĊH(CH2)3(CO2H) has been detected in a γ-irradiated single crystal of adipic acid. It has been calculated from the anisotropy of the spectra on rotation of the crystal that the radicals have almost the same orientation as the undamaged molecules, although the plane of the free radical carbon is twisted approximately 10° from the original plane of the three terminal carbon atoms.