T. Kumada et al., DECAY BEHAVIORS OF H-2(-) ANIONS IN SOLID PARAHYDROGEN - EFFECT OF NUCLEAR SPINS ON CHEMICAL-REACTIONS, JOURNAL OF PHYSICAL CHEMISTRY B, 101(7), 1997, pp. 1198-1201
Decay processes of H-2(-) anions in gamma-ray-irradiated solid parahyd
rogen were studied by using an ESR spectrometer. The following interes
ting results were obtained. First, the initial yields of ortho-H-2(-)
anions in the gamma-irradiated solid parahydrogen were 3 times as larg
e as those of para-H-2(-) anions. Second, the yields of para-H-2(-) an
ions decrease faster than those of ortho-H-2(-) anions upon storage of
the irradiated samples at 4.2 K. Third, the decay rate of H-2(-) anio
ns is accelerated by the addition of HD and D-2 molecules. Fourth, H-2
(-) anions at 2.2 K decay faster than at 4.2 K. According to the parit
y conservation rule in a homonuclear diatomic molecule, the energy of
ortho-H-2(-) anions at the ground state is lower than that of para-H-2
(-) anions, whereas that of ortho-H-2 molecules is higher than that of
para-H-2 molecules at low temperatures. The first and second results
are ascribed to para --> ortho conversion of H-2(-) anions. The third
result indicates that nearby HD and D-2 accelerate the decay of H-2(-)
anion or broaden the spectra by superhyperfine interactions. The four
th result suggests a coherent tunneling mechanism of decay of H-2(-) a
nions in the solid parahydrogen.