COLLISIONAL PUMPING - A TECHNIQUE FOR MEASURING FLUORESCENCE LIFETIMES OF OPTICALLY INACCESSIBLE STATES

A technique is presented for measuring both fluorescence lifetimes and vibrational relaxation rates from optically inaccessible levels. The technique involves preparing the levels by collisional transfer from an optically prepared state. The technique is demonstrated by measuring the fluorescence lifetimes of the 11(1), 16(2) and 0(0) levels of benzene, populated by collisional transfer from the 6(1) level using argon as the collision partner. The fluorescence lifetimes determined by this method are: 11(1) (86 +/- 2 ns), 16(2) (86 +/- 3 ns), and 0(0) (111 +/- 12 ns). The fluorescence lifetime of 6(1) was measured directly to be 88 +/- 2 ns. The 0(0) and 6(1) values are in accord with previously reported values obtained by direct optical pumping.