Electron-spin-resonance (ESR) signals attributed to the linear C6, C8, and C10 molecules in their lowest 3Σ states, presumably their ground states, have been observed in solid neon and argon matrices at 4 K. There is evidence of two forms of the C10 molecule, perhaps indicating two slightly bent structural isomers. Laser vaporization of graphite and 13C-enriched graphite produced a high proportion of these larger molecules. Hyperfine interaction in the 13Cn molecules was small and resolved only for C6, indicating cumulene-type bonding with the unpaired spins in pπ orbitals, as in C4. The zero-field-splitting parameters ‖D‖ were found to be 0.363, 0.783, and 0.190 cm−1, respectively, in solid neon. The increase in ‖D‖ through C8 is attributed to a corresponding variation in the spin–orbit coupling with low-lying states, principally the 1Σ+g, as the chains lengthen. Gross orbital spin populations and 1Σ+g– X 3Σ−g energy differences were obtained from Hartree–Fock calculations in order to interpret the hfs and ‖D‖ data, respectively. Electron correlation was included via second and third order Mo/ller–Plesset perturbation theory. The possibility of quasilinear or nonlinear character in these chains is briefly considered. Relative concentrations of the linear and cyclic forms of these molecules in the vapor and in matrices were estimated from thermodynamics using their theoretically derived properties.

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The X -band ESR spectrum of OdO was obtained in an argon.matrix at 4 OK as a series of 16 fine-structure lines between 0 and 12000 O. Analysis proved that most of these lines were due to off-principal-axis transitions and established the ground state as • I. An accurate fit to the data required the inclusion of a small b~ term (quartic in S,) besides the usual b~ = D term in the spin Hamiltonian. The derived parameters in an argon matrix are gil = 1.990(9).g,= 1.986(5).1 b~1 = ID 1 =0.2078(3) em-I. and 1 b~1 =0.00040(5) em-I. The two strongest lines were also observed in a neon matrix.

The absorption and magnetic circular dichroism spectra of the 2P+-2S transition of matrixisolated copper atoms have been measured in krypton and xenon matrices. A dramatic reversal in the MCD 'if' term pattern is observed. From a spectral band moment analysis it is shown that: (1) noncubic lattice cage vibrational motions are more important than cubic ones in contributing to the observed bandwidths and (2) the Cu excited state spin-orbit coupling constant (A) in krypton is reduced to 57% of its gas phase value, whereas in xenon it is reduced to -14% of its gas phase value. Calculations using the Moran model show that the excited state geometry of the metal/rare gas cage is distorted via the Jahn-Teller effect in opposite ways in krypton and xenon matrices. The negative sign of A in xenon reveals a reversal in the order of the 2 P state spin-orbit multiplets. Neither this reversal nor the reduction of A in krypton can be accounted for by the Jahn-Teller effect. We attribute the spin-orbit constant reduction to the overlap of the Cu 4p orbital with the np of the rare gas matrix cage atoms. The calculated spin-orbit reduction factors (in Ar, Kr, and Xe) agree well with the experimental ones if a contracted Cu 4p orbital is used. In the same way the ground state g factor shift with matrix atom type, observed by Kasai and McLeod, is semiquantitatively accounted for by calculation of the overlaps between the Cu 4s orbital and the np orbitals of the rare gas cage atoms.