Abstract

In the multiphoton ionization mass spectrum of CH₃OH induced by the XeCl laser, three kinds of ion are found: CH⁺₃, CH₂OH⁺, and CH₃OH⁺. The ionic signal dependences on the laser intensity and the sample pressure are measured. From these results, it is concluded that CH₃OH⁺ is directly formed after CH₃OH has absorbed four photons, and that the collisions between CH₃OH⁺ and CH₃OH produce ${\text{CH}}_3^{+}$ and CH₂OH⁺. At the same laser wavelength, the ions produced in the C₂H₅OH MPI process are ${\text{C}}_2{\text{H}}_5^{+}$, CH₂OH⁺, CH₃OH⁺, C₂H₂OH⁺, C₂H₃OH⁺, C₂H₄OH⁺, and C₂H₅OH⁺. The relative ionic intensities are 74%(CH₃OH⁺),$12\%\left({\text{C}}_2{\text{H}}_5^{+}\right)$, 6.1%(CH₂OH⁺), 4.1 %(C₂H₃OH⁺), and < 2% for others. On the basis of the consideration of the mass spectrum theory for organic molecules, brief explanations of the result are given. The breakdown of the C-O bond and the C-C bond results in the formation of ${\text{C}}_2{\text{H}}_5^{+}$; and CH₂OH⁺, respectively. The McLaffety rearrangement process leads to the production of C₂H₃OH⁺. The analysis shows that the birth of CH₃OH⁺ cannot be described in terms of the breakdown process of some molecular bonds; CH₃OH⁺ is the product of a very complicated recombination reaction.

© 1986 Optical Society of America