A study of light-induced proton transfer from gas phase (radical) cations to reference bases. Bracketing of proton transfer from excited ions and associated reaction kinetics.

By use of Fourier transform ion cyclotron resonance, it is shown that protonated naphthalene when excited with laser light of 488 nm is more reactive in proton transfer to reference bases than in its ground state. The excitation leads to reaction with bases for which proton transfer in the ground state is endothermic up to a detected maximum of 60 kJ/mol. For indene radical cations excited at 514.5 nm, it is shown that the rate constant for proton transfer to 3-pentanone is either about 10 or about 100 times lower than the rate constant for relaxation by collisions with 3-pentanone. From the energy deposited in the ions, 0.5-0.6 eV is available for proton transfer to a base which seems reasonable when taking into account a complete randomization of the initially deposited energy.