TRIPLET SPECIES FROM NORBORNADIENE - TIME-RESOLVED PHOTOACOUSTIC CALORIMETRY AND AB INITIO STUDIES OF ENERGY, GEOMETRY, AND SPIN-ORBIT COUPLING

摘要

The norbornadiene triplet is directly observed and its energy measured for the first time by time-resolved photoacoustic calorimetry. PAC affords a transient subsequent to the sensitizer triplet, with a lifetime of 6.20 +/- 0.03 ns and an energy of 61.37 +/- 0.25 kcal/mol relative to ND, which we have ascribed to the norbornadiene tripler. The lifetime of the triplet, which is anomalously short, is determined by the rate at which the species undergoes rearrangement along the path to quadricyclane. Calculations for the norbornene triplet indicate that its short lifetime is consistent with T-1 --> S-0 intersystem crossing. [References: 19]