Inspection of panel (b) in Figure shows that reaction between H and PH 3 (HT11) follows the Arrhenius behaviour. The rate constants computed from junChS-F12 and Best energy barriers are in remarkable agreement with the available experimental data, whereas the CBS-QB3 energy barrier leads to underestimated rate constants at low temperatures and overestimated rate constants at high temperatures. In this case the role af anharmonicity on the rate constants is negligible: for instance, the difference between harmonic and anharmonic (VPT2) ZPEs is about 0.3 kJ mol -1 . All these trends are confirmed by the coefficients of the Arrhenius-Kooij fittings collected in Table .