Abstract

Excitation of vibrations of chemical bonds in molecules is of considerable interest for controlling chemical reactions. Ever since the advent of the laser, chemists have been dreaming about the possibility to use laser light to selectively excite molecular bonds all the way up to the dissociation limit. Direct single photon excitation to a highly excited vibrational state is forbidden due to the very small overlap between the initial and final state. This necessitates a step-wise excitation. So far two complications have frustrated this quest for bond-selective chemistry. Firstly, the anharmonicity of a chemical bond makes it difficult to attain a high level of vibrational excitation: although the ground state can be depleted in favour of the first excited state upon irradiation with a precisely tuned laser, further excitation steps will require slightly different frequencies. Secondly, the time scale on which the vibrational energy in a given bond delocalizes by redistributing itself through the molecule is very short (picosecond range).

© 1994 Optical Society of America