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Electron spin resonance (ESR) studies are reported for Al16,17O, Ga16,17O, and In16,17O isolated in neon matrices at 4 K. Except for Al16O, no previous ESR measurements have been reported for these X 2Σ diatomic radicals. The pulsed laser vaporization of the metals in the presence of O162 and O172 produced high quality ESR spectra of these metal oxide radicals whose nuclear hyperfine interactions (A tensors) were fully resolved for both the metal and oxygen nuclei. An analysis of the experimental spin densities in combination with different types of theoretical calculations provided detailed information concerning the electronic structure trends going down this metal oxide group. Increased p-orbital spin density on oxygen was observed for the heavier metal oxide radicals. Nonrelativistic ab initio calculations with an extended basis set and the UB3LYP method reproduced the trends in the isotropic and dipolar hyperfine interactions. All-electron CI calculations, restricted open-shell Hartree–Fock (ROHF) wave functions, and unrestricted Hartree–Fock wave functions gave results very different from experiment and from each other for the isotropic interaction. All calculations were in fair agreement with each other for the dipolar interaction and provided an assignment of the sign for that term.

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The metal carbide radicals AlC and AlC2 have been generated by the laser vaporization of aluminum carbide and trapped in neon and argon matrices at 4 K for electron spin resonance (ESR) characterization. These results provide the first experimental evidence showing that AlC has a 4Σ ground electronic state and that AlC2 is X 2A1. Ab initio theoretical calculations were conducted for the geometries and various nuclear hyperfine parameters in both radicals which yielded A values in reasonable agreement with the observed. In AlC, the three unpaired electrons reside primarily on carbon with the following neon matrix magnetic parameters (MHz): g∥=2.000(1); g⊥=2.0010(5); ‖A⊥(Al)‖=33.2(5); ‖A∥(Al)‖=3(3); A⊥(13C)=52.1(5); A∥(13C)=52(2); and D(zero field splitting)=374(1). For AlC2, the spin density resides predominantly in an aluminum 3pz/3s hybrid directed away from C2. The neon magnetic parameters (MHz) are: g∥=2.0005(5); g⊥=1.9965(3); A⊥(Al)=941.5(5); A∥(Al)=1067(1); ‖A∥(13C)‖=59(1); and ‖A⊥(13C)‖=52(1).

An investigation of collisional processes in a Dicke narrowed transition of water vapor in the 7.8 μ m spectral region by frequency down-chirped quantum cascade laser spectroscopy