A remarkable temperature dependence of the rate constant for the tunneling reaction HD + D → H + D2 in the low temperature region 2.6–6.5 K

Rate constants for the tunneling reaction, HD + D → H + D2, in solid HD have been determined by using ESR in the very low temperature range of 2.6–6.5 K. The rate constants increase steeply with increasing temperature above 5 K, while they are almost independent of temperature below 5 K. The results above 5 K do not coincide with theoretical values calculated by the gas phase model. A phonon-assisted mechanism is proposed to account for the remarkable temperature dependence of the tunneling reaction in solid HD.