Realtime observation of the desorption process of isobutene from zeolite using picosecond infrared lasers

The transient absorption spectra of OD stretching mode of isobutene-adsorbed hydroxyl groups of DM20 zeolite were measured by picosecond infrared–infrared pump–probe experiment. The vibrational relaxation time (T1) of the v=1 state was estimated to be 12±2 ps from the temporal profile of the bleaching and hot bands of the OD stretching mode. We found a band indicating the production of a short-lived species at 40 ps after excitation. Moreover we observed the course of isobutene-desorption in the time region from 40 to 100 ps. This result implies that this desorption does not occur immediately but occurs after local vibrational relaxation.