Microhydration of Guanine base pairs.

We report spectroscopy of clusters of guanine base pairs with one and two water molecules. We recorded the vibronic spectra of the mass-selected GG(H2O) and GG(H2O)2 clusters using resonant two photon ionization (R2PI) and we used IR-UV double resonance spectroscopy to obtain ground state IR spectra of these clusters. We found that a single water molecule stabilizes one of two structures we had previously found for guanine dimers. Addition of a second water molecule causes no further structural change.