Multiphoton metastable ion spectra and ion dissociation kinetics: Analysis of the decay channels of the aniline cation with a reflectron time-of-flight instrument

Multiphoton mass spectrometry when carried out in conjunction with a reflecting field time-of-flight mass spectrometer is shown to yield rich new metastable ion spectra of polyatomic molecules, here aniline. The reflecting field acting also as an energy analyzer is shown to be particularly suitable for sensitive metastable ion detection without interference from stable fragment ions. With this technique several new metastable ion decay channels of the aniline cation have been observed. On the basis of the measured metastable ion spectrum a reasonable fragmentation pathway for the aniline cation C6H7N+ after multiphoton excitation is presented. The prominent intensity of the metastable ion peak C5H+6 points to a narrow energy distribution within the aniline cation typical for a ladder switching multiphoton excitation mechanism.