The Continuing Search for One Photon State Selective Vibrational Chemistry

A tantalizing goal, the unambiguous demonstration of state selective chemistry, is being actively pursued by several research groups.1 Bond selective chemistry has promise for the production of unique chemical species. First it must be shown that nonstatistical rates of reactions can be induced. Progress in this field has been moderately encouraging in that the systems studied are suggestive of small rate enhancements. The best case observed is the isomerization of allylisocyanide to allycyanide by Reddy and Berry.2 This unimolecular reaction was initiated with a single photon corresponding to the energy of a C-H overtone stretching vibration. The three different C-H bonds were excited with varying quanta and a direct correlation between the bond excited and the rate of isomerization was observed. When the isomerization rates are compared to the theoretical "thermal" expectations (RRKM) it is concluded that the overtone vibrational energy has not been throughly redistributed on the time scale for reaction.