Infrared Spectroscopy of Jet Cooled Biological Molecules with Diode Lasers

Abstract

A direct absorption experiment has been developed to study hydrogen bonding in nucleotide base clusters. A high temperature pulsed slit molecular beam source has been constructed allowing a sample to be heated to $250^{\circ}C$. The resulting supersonic expansion is probed by tunable infrared Pb-salt diode lasers using a Herriott multi-pass cell. The first step in studying these clusters is to characterize the intramolecular vibrational modes of the monomeric bases. To this end. we have observed the first rotationally resolved vibrational spectrum of uracil, one of the four bases of RNA. This band was observed near $1700 cm^{-1}$ and corresponds to a carbonyl stretch. Following spectroscopic characterization of uracil monomer, we plan to study the intermolecular modes within uracil-water and uracil-clusters. We will eventually expand this work to include other RNA and DNA bases.