B-2U-]A(1G) FLUORESCENCE EXCITATION SPECTRUM OF LIQUID BENZENE FROM 250 TO 150 NM

The B-2u --> A(1g) fluorescence quantum yield of benzene has been obta ined for excitations from 250 to 150 nm in the solvents n-hexane, isoo ctane, n-perfluorohexane, n-pentane, cyclohexane, and cis-decalin. In n-hexane and isooctane, measurements have been made over a range of be nzene concentrations from 0.11(2) to 11.2 M (the neat liquid). In dilu te solutions, the sudden losses in fluorescence as the excitation wave length sweeps from the first into the second absorption system and the n again as the excitation wavelength sweeps from the second into the t hird absorption system are correlated with the behavior of benzene vap or in the region of channel three. Increasing the benzene concentratio n causes abatements in;he rate of loss of fluorescence with decreasing excitation wavelength in the regions of the second and third absorpti on systems and, above 2 M, causes a reversal of this,rate so as to cau se a recovery of the fluorescence in the region of the third absorptio n system. These changes are correlated with the effects of benzene con centration on the electronic absorption spectrum and with reported eff ects of clustering on the multiphoton photoionization efficiency.