Reaction of H with highly vibrationally excited water: activated or not?

The Dynamics of the H+H2O Reaction

“…Immediately, it can be seen that the QCT results using the I5 PES are orders of magnitude higher than the experimental rate coefficients. As noted by Schatz and co-workers, [36,70] this is a consequence of the too low threshold energy for the (00) and (01) AE states on the I5 PES. On the contrary, the QCT rate coefficients using the OC PES and the WSLFH PES are in accordance with the experiments.…”

“…On the contrary, the first piece of evidence that the OC PES needed to be improved was given by Schatz et al, [36] who studied the reactive and nonreactive dynamics of H atoms with vibrationally excited H 2 O molecules. In that work, high-quality ab initio calculations were performed in the rectant region that corresponds to high OH stretch excitations, and they concluded that the OC PES was too attractive at long range.…”

“…Also, rate coefficients are a challenge to Quantum Chemistry theory because they are sensitive to the height and width of the barrier of the PES. QCT rate coefficients have been calculated by Schatz et al using the I5, [70] the OC, [36] and the WSLFH PESs. [37] Interestingly, they found that the thermal rate coefficients are generally dominated by vibrationally excited states of H 2 O.…”

“…However, specific rate coefficients for the (02) À , (03) À , and (04) À states of H 2 O are significantly larger on the OC PES than on the WSLFH PES. [36] QCT calculations of the integral cross-sections as a function of collision energy showed that the OC PES have a nonzero threshold energy for these states, whereas in the WSLFH PES the threshold is nearly zero. This behavior on the OC PES was attributed to a too broad long-range attractive potential [36] that is narrower in accurate ab initio calculations and on the WSLFH PES.…”

“…[36] QCT calculations of the integral cross-sections as a function of collision energy showed that the OC PES have a nonzero threshold energy for these states, whereas in the WSLFH PES the threshold is nearly zero. This behavior on the OC PES was attributed to a too broad long-range attractive potential [36] that is narrower in accurate ab initio calculations and on the WSLFH PES. [37] The QCT method has several shortcomings, such as its inability to describing tunneling or the ZPE leaking problem mentioned above.…”