The photodissociation of some alkyl iodide cations

Photodissociation of the molecular ions CH3I+, CD3I+, C2H5I+, and n-C3H7I+ and of the radical ion ⋅CH2I+, has been studied using a tandem quadrupole mass spectrometer and a flashlamp pumped tuneable dye laser. Predissociation of CH3I+ and CD3I+ results in very detailed spectra, which are assigned, and which permit measurement of, vibrational frequencies for the ? states of these ions. The spectra for C2H5I+, n-C3H7I+, and ⋅CH2I+ consist of broad and structureless bands. In the case of C2H5I+ this is believed to be due to the very short lifetime of a predominating ? state, while in n-C3H7I+ the dissociation is thought to arise from direct transitions between the two lowest states of the ion which are analogous to the spin–orbit components in CH3I+. In the case of the ⋅CH2I+ radical, the lack of structure is attributed to the formation of the primary ion with a wide spread in internal energies.