ESR OBSERVATION OF THE H-CENTER-DOT-CENTER-DOT-CENTER-DOT-H, H-CENTER-DOT-CENTER-DOT-CENTER-DOT-D, AND D-CENTER-DOT-CENTER-DOT-CENTER-DOT-D SPIN-PAIR RADICALS IN RARE-GAS MATRICES

The first experimental observation of the fundamentally important spin-pair radicals, H ... H, H ... D, and D ... D is reported. ESR (electron spin resonance) studies of rare gas matrices near 4 K containing extremely high concentrations of H and D atoms revealed the presence of these spin exchange-coupled molecules whose ESR spectra are analyzed in terms of a (3) Sigma electronic ground state. The observed D tenser (zero-field splitting) for a specific isotopic spin pair was surprisingly constant in all four rare gases but showed large changes among the three isotopic species. As expected, the hyperfine splitting (A(iso)) for the spin-pair was observed to be one-half that of the free H or D atom. (C) 1995 American Institute of Physics.