Excited state spectroscopy and dynamics of isolated adenine and 9-methyladenine

Abstract
We report electronic spectra of the DNA base adenine and its derivative 9-methyladenine in a molecular beam, using [1 + 1] resonantly enhanced multiphoton ionisation. In addition an excited state lifetime of adenine was determined by picosecond time-resolved [1 + 1′] photoionisation. The spectrum of adenine is dominated by a band at 36105 cm−1, with several low-frequency bands nearby. A comparison with the spectrum of 9-methyladenine with its origin at 36136 cm−1 confirms that the electronic spectrum of adenine is dominated by the π → π* transition of the N9–H tautomer. Several bands observed before and assigned to a n → π* transition were not observed. For the most intense band of adenine at 36105 cm−1 we determined an excited state lifetime of 9 ps.

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