The mid-IR absorption spectrum of gas-phase clusters of the nucleobases guanine and cytosine

The mid-infrared (IR) absorption spectrum of jet-cooled clusters of the nucleobases guanine and cytosine has been recorded in the 500–1800 cm−1 range by ion-dip spectroscopy. Some 30 clearly separated and sharp resonances are observed. The combination of the experimental data with new high-level ab initio calculations is consistent with a previous structural assignment and a tentative assignment is made to the K7-1E structure of guanine–cytosine. These data can serve as a test of the method in the mid-IR regime.