UV excitation of isolated singly-charged deprotonated mononucleotide anions in the gas phase can lead to their dissociation. We present mass spectrometry results, photodepletion and photofragment action spectra on the UV-photodissociation of deprotonated 2'-deoxyribonucleobase-5'-monophosphates with adenine, cytosine, guanine and thymine as nucleobases. We observe the same anionic fragments as in earlier experiments on collision-induced dissociation, although their relative intensities are quite different, especially with respect to the abundance of the deprotonated base anions. The fragment channels correspond to loss of genetic information by cleavage of the CN glycosidic bond and to strand breaking by severing the phosphate-sugar link. We compare the photodissociation spectra with UV absorption spectra of aqueous solutions of the same species and discuss the photodissociation behavior in the context of possible mechanisms and ergodic versus non-ergodic fragmentation.

We report photodissociation action spectra for the dianion IrBr(6)(2-) in the range of 1.08-5.6 eV. The photoproducts observed are IrBr(6)(-), IrBr(5)(-), IrBr(4)(-) and Br(-). Comparison of the action spectra to the aqueous absorption spectrum of K(2)IrBr(6) leads to the determination of solvatochromic shifts of between 0.02 and 0.16 eV in the visible region and approximately 0.3 eV in the ultraviolet. The fragmentation branching ratios vary greatly as a function of photon energy. This behavior can be attributed to differences in the fragmentation mechanisms as well as differences in the excited states that are accessed at different energies. Absorption in the visible region favors fragmentation into IrBr(5)(-) and Br(-), whereas a number of fragmentation channels and mechanisms are active in the ultraviolet region. These mechanisms include fragmentation as well as electron detachment and dissociative electron detachment.

We present experimental infrared spectroscopic data on mass-selected, hydrated nitromethane anion clusters with up to four water ligands. The vibrational bands in the OH stretching region encode the solvent structure, while the CH stretching bands contain information on the influence of the hydration shell on the solute ion. We interpret our findings using density functional theory calculations. The first water molecule binds symmetrically to the two oxygen atoms of the nitro group but couples to low-frequency vibrational modes that impart a very complicated structure on the OH stretching region. Competition between water-ion and water-water interaction makes the dihydrate very floppy and precludes unambiguous structural assignment. The tri- and tetrahydrate spectra can be interpreted on the basis of H-bonded ring structures. The excess electron is polarized by hydration, which can clearly be seen by shifting CH stretching frequencies.