Theoretical study of the chemiluminescence of the Al + H2O reaction

We performed surface hopping simulations of Al + H2O collisions by a direct semiempirical method, reproducing the conditions of previous beam-gas experiments. We observed the formation of the HAlOH species, that dissociates to AlOH + H after a lifetime of about 0.6 ps. This species undergoes nonadiabatic transitions to its first excited state and is responsible for chemiluminescence in the visible range, while the Al−H2O complex emits in the infrared. The computed emission band in the visible is red-shifted with respect to the experimental one, because of slight inaccuracies of the potential energy surfaces. However, collisions with more water molecules and exciplex formation with excited Al(2S, 4P) atoms may also contribute to the short wavelength emission, as we show by accurate ab initio calculations.