Using synchrotron-generated vacuum-ultraviolet radiation and multiplexed time-resolved photoionization mass spectrometry we have measured the absolute photoionization cross-section for the propargyl (C(3)H(3)) radical, σ(propargyl) (ion)(E), relative to the known absolute cross-section of the methyl (CH(3)) radical. We generated a stoichiometric 1:1 ratio of C(3)H(3):CH(3) from 193 nm photolysis of two different C(4)H(6) isomers (1-butyne and 1,3-butadiene). Photolysis of 1-butyne yielded values of σ(propargyl)(ion)(10.213 eV)=(26.1±4.2) Mb and σ(propargyl)(ion)(10.413 eV)=(23.4±3.2) Mb, whereas photolysis of 1,3-butadiene yielded values of σ(propargyl)(ion)(10.213 eV)=(23.6±3.6) Mb and σ(propargyl)(ion)(10.413 eV)=(25.1±3.5) Mb. These measurements place our relative photoionization cross-section spectrum for propargyl on an absolute scale between 8.6 and 10.5 eV. The cross-section derived from our results is approximately a factor of three larger than previous determinations.

The electronic spectra of cold protonated aromatic amines: anilineH(+) C6H5-NH3(+), benzylamineH(+) C6H5-CH2-NH3(+) and phenylethylamineH(+) C6H5-(CH2)2-NH3(+) have been investigated experimentally in a large spectral domain and are compared to those of their hydroxyl homologues. In the low energy region, the electronic spectra are similar to their neutral analogues, which reveals the ππ* character of their first excited state. A second transition is observed from 0.4 to 1 eV above the origin band, which is assigned to the excitation of the πσ* state. In these protonated amine molecules, there is a competition between different fragmentation channels, some being specific to UV excitation i.e., not observed in low-energy collision induced dissociation experiments. Besides, for one amine a drastic change in the fragmentation branching ratio is observed within a very short energy range that reveals the complex excited state dynamics and fragmentation processes. The experimental observations can be rationalized using a simple qualitative model, the ππ*-πσ* model [A. L. Sobolewski, W. Domcke, C. Dedonder-Lardeux and C. Jouvet, Phys. Chem. Chem. Phys., 2002, 4, 1093-1100], which predicts that the excited state dynamics is controlled by the crossing between the ππ* excited state and a πσ* state repulsive along the XH (X being O or N) coordinate.