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Paramagnetic resonance absorption has been observed in naphthalene in solid solution in a single crystal of durene when irradiated with light from an A-H6 mercury lamp. The fine structure of the spectrum at a frequency of ∼22.7×109 cps may be described by the spin-Hamiltonian H=|β|H·g·S+DSz2+E(Sx2−Sy2),,with S=1,g=2.0030±0.0004 (isotropic),D/hc=±0.1003±0.0006 cm−1,E/hc=∓0.0137±0.0002 cm−1.Observations at a different frequency, ∼9.7×109 cps, and also measurements on perdeuteronaphthalene are described by essentially the same parameters. The fine structure data identify the spectrum as arising from a triplet state and leave no doubt as to the triplet character of the phosphorescent state of naphthalene. The zero-field splitting of the triplet has its origin in the magnetic dipole-dipole interaction between the two unpaired electrons in the triplet state. These experimental results are in agreement with the theoretical estimates. Hyperfine structure has been observed and is interpretable on the basis of the anisotropic hyperfine interaction constants for a C–H fragment given by McConnell. The π-electron spin density on the α-carbons is found to be 0.209. The hyperfine structure results identify the spectrum as arising from naphthalene. In addition they show that the triplet state is 3B2u+ and that the naphthalene molecules are oriented in the crystals such that they are not only coplanar with the durene molecule which they replace but also have their long and short twofold axes in this plane parallel, respectively, to the long and short axes of durenes.

Nitrogen and deuterium nuclear quadrupole resonance in lanthanum nicotinate dihydrate Deuteron, proton, and sodium magnetic resonance study of sodium bromide dihydrate and sodium chloride dihydrateThe EPR (electron paramagnetic resonance) and proton ENDOR (electron nuclear double resonance) spectra of single crystals of lanthanum nicotinate dihydrate with Nd+ 3 dilutely substituted for La+ 3 have been obtained and described by appropriate spin Hamiltonian operators. The ENDOR signals of protons lying within 5 A of the Nd+ 3 have been resolved and assigned to specific protons. The physical interpretation of the measured anisotropic rare earth ion-proton hyperfine interactions has been given. The spatial coordinates of the protons in the principal axis system of the electron Zeeman interaction matrix g.have been obtained with standard deviations ranging from 0.002 to 0.015 A, with an average of 0.006 A.The average standard deviation for the coordinates of the 4 H 2 0 protons nearest to the Nd + 3 ion, three of which form hydrogen bonds with nicotinate nitrogen atoms, is 0.004 A. The average standard deviation for their distances from the Nd+ 3 is 0.003 A. It is clear that by means of suggested improvements of the reported techniques it should be possible to measure proton coordinates to 0.001 A. The methods developed show promise for applications to problems concerning the structure of organic molecules, in particular organo-metallic complexes and large molecules of biological interest, such as proteins, to which paramagnetic ions may be attached.It is well-known that in ions of the lanthanide elements the I-electrons are highly localized in the vicinity of the nucleus. 8 -10 Consequently, it may be anticipated that in the case of a complex of an organic molecule and a rare earth ion, the electronic magnetic mo-

Paramagnetic resonance absorption of all the naturally occurring rare earth trivalent ions in the LaCh structure have been investigated. The results are summarized in the form of a tabulation of the parameters gil, gl, A, B, P, Ll in the spin-Hamiltonian. Theoretical calculations of crystal field states and eigenvalues as well as of gil and gl, based on optical measurements, are discussed.

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LETTERS TO Nucleus Sr 90 Sr 91 Y 90 Y 91 Sb 125 Cs 137 (W> 2 -1)/*X10 10 0.4 0.7 0.3 0.8 1.1 1.8The criterion fits Sr 89 and K 42 ; in both cases shell model considerations support the assignment Al-±2 and change in parity. An excellent measurement of K 42 has already been made by Siegbahn. 9 It disintegrates ( Fig. 1) by negatron emission to the ground state of Ca 42 and also to an excited state followed by a gamma-ray. We have analyzed Siegbahn's data for the high energy component with results shown in Fig. 2 both for an allowed FK plot and again as a forbidden FK plot wherein the factor G is included. The bulging curvature of the one and the near-straightness of the other confirm the above-stated criterion as well as those aspects of the shell model and of the Fermi theory of beta-decay which are involved in this example.The shell model associates the odd configuration (3d) -1 (4/) 3 with the ground state of K 42 . Similarly the even configuration (4/) 2 may be associated with the ground state of Ca 42 (probably 1 = 0) and with low excited states (1=2, 4, and 6). We suggest 1 = 2 and even parity for the excited state of Ca 42 observed in the K 42 decay. The low energy transition is thus interpreted as first-forbidden with A/ = 0. * Assisted by the joint program of the ONR and the AEC. iE.

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The anisotropic proton hyperfine interaction of the triplet-state electrons of the naphthalene molecule have been measured at the boiling point of N2. The naphthalene molecules were oriented in single crystal solid solutions in durene. The effects of various substitutions of D for H were investigated. The spin density distribution deduced from these experiments was ρα=+0.219, ρβ=+0.062, ργ=—0.063. These results were compared with the results of theoretical calculations and with experimental results for the naphthalene negative ion.