title: Vibrational spectroscopy of anionic nitrate complexes of UO22+ and Eu3+ isolated in the gas phase.
abstract: Wavelength-selective infrared multiple photon photo-dissociation (IRMPD) was used to generate spectra of anionic nitrate complexes of UO(2)(2+) and Eu(3+) in the mid-infrared region. Similar spectral patterns were observed for both species, including splitting of the antisymmetric O-N-O stretch into high and low frequency components with the magnitude of the splitting consistent with attachment of nitrate to a strong Lewis acid center. The frequencies measured for [UO(2)(NO(3))(3)](-) were within a few cm(-1) of those measured in the condensed phase, the best agreement yet achieved for a comparison of IRMPD with condensed phase absorption spectra. In addition, experimentally-determined values were in good general agreement with those predicted by DFT calculations, especially for the antisymmetric UO(2) stretch. The spectrum from the [UO(2)(NO(3))(3)](-) was compared with that of [Eu(NO(3))(4)](-), which showed that nitrate was bound more strongly to the Eu(3+) metal center, consistent with its higher charge. The spectrum of a unique uranyl-oxo species having an elemental composition [UO(9)N(2)](-) was also acquired, that contained nitrate absorptions suggestive of a [UO(2)(NO(3))(2)(O)](-) structure; the spectrum lacked bands indicative of nitrite and superoxide that would be indicative of an alternative [UO(2)(NO(3))(NO(2))(O(2))](-) structure.
authors.affiliation: Idaho National Laboratory, Idaho Falls, ID, USA. gary.groenewold@inl.gov
authors.forename: G S
authors.initials: GS
authors.lastname: Groenewold
authors.forename: J
authors.initials: J
authors.lastname: Oomens
authors.forename: W A
authors.initials: WA
authors.lastname: de Jong
authors.forename: G L
authors.initials: GL
authors.lastname: Gresham
authors.forename: M E
authors.initials: ME
authors.lastname: McIlwain
authors.forename: M J
authors.initials: MJ
authors.lastname: Van Stipdonk