The Multiphoton Ionization Spectrum of Methyl Iodide Revisited: 1.67-2.2 ev Excitation

Abstract

The study of the multiphoton ionization of methyl iodide has a long and storied history. Here, we revisit this topic and present spectra of each of the photoionization and photodissociation fragments ($C^{+},$ $CH^{+},$ $CH_{2}^{+},$ $CH_{3}^{+},$ $CH_{3}I^{+},$ and $I^{+}$) using a custom time-of-flight mass spectrometer and a tunable dye laser over the excitation range of 550-740 nm (2.2-1.67 eV). The choice of this wavelength range allows for excitation through the $A$ state and resonant ionization through higher energy levels using 4+1, 5+1, or 6+1 photons for excitation and ionization.  Although the various fragments yield very similar spectra, fewer fragment ions are observed with increasing wavelength.