Abstract

Hole burning in mixed crystals containing methyl groups can be used to determine the difference of the rotational tunnel splitting of the methyl groups in the ground and excited electronic state of the guest probe /1/. Two mechanisms were suggested: If the phototransformation of the probe is photochemical in nature, the difference in tunnel splitting shows up in the side hole pattern which appears upon thermal relaxation of the bleached ground state levels through spin conversion processes. On the other hand, if the phototransformation is purely photophysical in nature, the nuclear spin conversion occurs most probably in the excited triplet state and the tunnel splitting is reflected in the appearance of antiholes.

© 1991 Optical Society of America