  In this work, we demonstrate measurements of photodestruction rates of
translationally cold, charged biomolecules. The long-term stable storage of the
molecular ions in an ion trap at ultra-high vacuum conditions allows
measurement of small rates and verification that rates are linear in
photodestruction laser intensity. Measurements were performed on singly
protonated molecules of the organic compound glycyrrhetinic acid (C30H46O4),
dissociated by a continuous-wave UV laser (266 nm) using different intensities.
The molecules were sympathetically cooled by simultaneously trapped
laser-cooled barium ions to translational temperatures of below 150 mK.
Destruction rates of less than 0.05 s^-1 and a cross section of (1.1 +/- 0.1) *
10^-17 cm^2 have been determined. An extension to tunable UV laser sources
would permit high-resolution dissociation spectroscopic studies on a wide
variety of cold complex molecules.
