Excited-State Relaxation of Protonated Adenine

The excited state dynamics of protonated adenine in the gas phase were investigated by femtosecond pump–probe transient mass spectroscopy. Adenine was protonated in an electrospray ionization source and transferred to a Paul trap. Two femtosecond laser pulses at 266 nm and 800 nm excited the lowest electronic ππ* state and probed the excited‐state dynamics by monitoring ion fragment formation. The measured excited state decay is monoexponential with a lifetime shorter than 161 fs. This agrees with a theoretical prediction of very fast internal conversion via a conical intersection with the ground state. Photostability of adenine: Femtosecond pump–probe transient mass spectrometry was used to investigate the excited‐state dynamics of protonated adenine in the gas phase. Fragmentation patterns are similar to those found for high‐energy collision‐induced dissociation mass spectra, and experimental evidence agrees well with predictions that a conical intersection to the ground state is accessed without a barrier.