Absolute Photoionization Cross Section and Dissociative Ionization Pathways of Alpha-Pinene

The absolute photoionization cross section of the monoterpenoid, alpha-pinene (AP), is presented together with the relative photoionization cross sections of its dissociative fragments for the first time. Experiments are performed via multiplexed vacuum ultraviolet (VUV) synchrotron photoionization (PI) mass spectrometry in the 8.0-11.0 eV energy range. Experimental work is conducted at the Advanced Light Source of the Lawrence Berkeley National Laboratory. Dissociative fragments were identified at m/z 121, 94, 93, 92, and 80. The photoionization cross section for the parent mass at 11.0 eV was determined to be 17 +/- 4 Mb with a total ionization cross section of 92 +/- 23 Mb at the same photon energy. Experimental appearance energies of dissociative ionization fragments and potential dissociative ionization pathways calculated at the G4 level of theory are presented as well. The photoionization cross section of alpha-pinene (AP) has been measured for the first time using multiplexed synchrotron photoionization mass spectrometry in the 8.0-11.0 eV energy range. At 11.0 eV the photoionization cross section of AP has a relatively small cross section of 17 +/- 4 Mb as compared to the total cross section of 92 +/- 23 Mb due to its large fragmentation, mainly, into the daughter ions m/z 92 and 93 (meta- and para-toluenium ions). image