Intersystem crossing in isolated molecules. Magnetic field effects on the fluorescence decay behavior of1B3upyrazine with lsquo;lsquo;singlersquo;rsquo; rovibronic level excitation

摘要

Coherently prepared lsquo;lsquo;singlersquo;rsquo; rovibronic levels of electronically excited pyrazine typically exhibit a biexponential fluorescence decay whose preexponential factor ratioA+/Aminus;is magnetic field dependent. Studies of this dependence for differentJprime; values show that complete spin decoupling from the molecular frame, leading to the intersystem crossing (ISC) selection rule Dgr;J=0,plusmn;1, occurs at the anomalously low field of sim;100 G. The monoexponential decay of theJprime;=0 level is independent of the field. An analysis of these results suggests that Coriolis coupling plays an important role in the ISC process, a fact which explains the magnetic quenching behavior of many polyatomic molecules.