Nanosecond Versus, Picosecond Molecular Multiphoton Fragmentation of Ketene and Cyclohexane

Abstract

Multiphoton dissociation of ketene was studied at 290.5 nm after irradiation of the first excited singlet state with two different laser pulsewidths of 4 ns and 10 ps. Analysis of the photofragment fluorescence spectra in the two time domains sheds light on the mechanisms that are responsible for the production of the observed CH(A2Δ),  (B2Σ−) and C2(d3Πg) photofragments. Multiphoton ionization of cyclohexane induced by a visible laser at 581 nm and its second harmonic at 290.5 nm was measured in the above mentioned pulse duration regimes. Study of the dependence of the total ionization signal on pressure and laser energy helps to clarify the role played by the giant resonance of this molecule at 84000 cm-1 in the photoionization process.