Analysis of the Photo Conversion of Asphaltenes Using Laser Desorption Ionization Mass Spectrometry: Fragmentation, Ring Fusion, and Fullerene Formation

Abstract

The conversion or photo conversion of asphaltenes to polycyclic aromatic hydrocarbons (PAH's) promoted by a laser source is analyzed using both experimental and theoretical methods. We propose that during measurements performed at an intermediate laser power, fragmentation to afford PAH's and ring fusion to yield fused PAH's (FPAH's) may occur either within molecular clusters (resin case) or within molecular aggregates (asphaltene case) which are vaporized or sublimed after ionization by the laser source. These events change the initial molecular mass distribution (MMD) of the sample to a continuous statistical MMD that can be fitted to a log-normal distribution. At a high laser power, the experimental MMD is converted to a sequence of Cn bands (n is an even number) which are separated by a 24-amu, the characteristic of a mixture of fullerene compounds.