The Baer Group has published a threshold photoelectron photoion coincidence study in which the energy required to dissociatively ionize propene (C3H6 + hv → C3H5+ + H + e-) was measured to be 11.898 ± 0.024 eV. When this is combined with a recently reported ionization energy of the allyl radical, see Figure below, a high precision propene C-H bond energy (BE) as well as the proton affinity (PA) of allene could be established.
This study was complicated by the slow dissociation of the propene ion, which caused previous investigations to be too high, thereby underestimating the PA and overestimating the BE. The Baer group established the correct dissociation onset by measuring the dissociation rate constants as a function of the ion energy by time of flight mass spectrometry, and extrapolating the rate to the dissociation onset.
The Baer Group, in collaboration with Prof. Laura Clarke with NSCU Physics department, as published in The Journal of Physical Chemistry C, has discovered some interesting long-term growth dynamics when organic molecules deposit on a surface. These studies are important because airborne organic molecules routinely deposit onto surfaces ranging from aerosol particles to buildings and interior walls. The surface-bound organics impact the environment in many ways. In the case of aerosols, organic coatings may affect reactive, hygroscopic, and radiative properties.
Deposition of airborne organic species onto buildings and historical monuments contributes to black crusts that must be removed for aesthetic reasons as well as for the preservation of the structure. In a controlled study, postdoc Eva Garland investigated oleic acid, which is frequently found in the atmosphere, on a silica surface, and found that the morphology can change over the period of several weeks. Initially, the oleic acid forms small 100 nm sized droplets on the surface. But they grow in time, and sometimes form strange structures as seen in the atomic force microscope (AFM) image. Eventually, they form very large islands, which appear to be thermochemically most stable.