Dynamics of infrared photodissociation of methanol clusters in zeolites and in solution

We have investigated the dynamics of the O-H stretch vibration of clustered (hydrogen-bonded) methanol molecules in solution and in Na-zeolites with time-resolved (picosecond) pump-probe infrared spectroscopy. It is shown that in both cases, after resonant IR excitation, vibrational relaxation occurs by breaking the hydrogen bond between the methanol molecules. This process occurs much faster in solution (T-l less than or equal to 3 ps) than inside the zeolite (T-l=10+/-3 ps). A second remarkable difference is that whereas in solution a rapid hydrogen-bond reassociation occurs (tau(r)=25+/-3 ps), in the zeolite this process takes considerably longer (tau(r) much greater than 2 ns).