Dependence of the laser two-photon ionization signal of anthracene on the electron mobility and the excess energy in non-polar solvents

The photocurrent and photoionization charge of anthracene in various non-polar solvents have been measured under the thirdharmonics of a Nd-YAG laser excitation. They are quadratically proportional to the laser pulse energy, though those of water are cubically proportional to them. Anthracene exhibited a larger signal in those solvents in which both the electron mobility and the excess energy are large. Such solvents offered a higher sensitivity for the photoionization technique. Degassing showed only a minor effect. The detection limits were 14 ng/dm3 (ppt) in hexane and 3.0 ng/dm3 (ppt) in 2,2,4-trimethylpentane.