Infrared photodissociation spectroscopy of microhydrated nitrate-nitric acid clusters NO3(-)(HNO3)(m)(H2O)(n).

Infrared multiple photon dissociation (IRMPD) spectra of NO3(-)(HNO3)m(H2O)n(H2)z with m = 1-3, up to n = 8 and z ≥ 1, are measured in the fingerprint region (550-1880 cm(-1)), directly probing the NO-stretching modes, as well as bending and other lower frequency modes. The assignment of the spectra is aided by electronic structure calculations. The IRMPD spectrum of the m = 1, n = 0 cluster is distinctly different from all the other measured spectra as a result of strong hydrogen bonding, leading to an equally shared proton in between two nitrate moieties (O2NO(-)···H(+)···ONO2(-)).

Vibrational spectroscopy of bisulfate/sulfuric acid/water clusters: structure, stability, and infrared multiple-photon dissociation intensities.

The structure and stability of mass-selected bisulfate, sulfuric acid, and water cluster anions, HSO4(-)(H2SO4)m(H2O)n, are studied by infrared photodissociation spectroscopy aided by electronic structure calculations. The triply hydrogen-bound HSO4(-)(H2SO4) configuration appears as a recurring motif in the bare clusters, while incorporation of water disrupts this stable motif for clusters with m > 1. Infrared-active vibrations predominantly involving distortions of the hydrogen-bound network are notably missing from the infrared multiple-photon dissociation (IRMPD) spectra of these ions but are fully recovered by messenger-tagging the clusters with H2.

Communication: Vibrational spectroscopy of atmospherically relevant acid cluster anions: bisulfate versus nitrate core structures.

Infrared multiple photon dissociation spectra for the smallest atmospherically relevant anions of sulfuric and nitric acid allow us to characterize structures and distinguish between clusters with a bisulfate or a nitrate core. We find that bisulfate is the main charge carrier for HSO(4)(-)·H(2)SO(4)·HNO(3) but not for NO(3)(-)·H(2)SO(4)·HNO(3). For the mixed dimer anion, we find evidence for the presence of two isomers: HSO(4)(-)·HNO(3) and NO(3)(-)·H(2)SO(4).