Simultaneous advances in gas phase spectroscopy and computational chemistry have made it possible to study isolated DNA base pairs. This account focuses on three specific topics that have emerged from this research, namely (i) the use of experimental data as benchmarks for theory, (ii) base pair structures, and (iii) the dynamics of the electronically excited state. The lowest energy nucleobase pair structures are not always observed in gas phase spectroscopy. One possible reason may be short

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... cited state lifetimes in certain structures. This explanation is consistent with theoretical models and with the observation that the isolated guanine cytosine (GC) Watson-Crick structure exhibits a different photochemistry than other hydrogen bonded GC structures