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Zinc nitrate anion complexes, [Zn(NO 3 ) 3 ] − and [ZnO(NO 3 ) 2 ] − , were generated by electrospray ionization and studied by tandem mass spectrometry. Dissociation of [Zn(NO 3 ) 3 ] − yields two direct fragments, [ZnO(NO 3 ) 2 ] − and NO 3 − . In contrast, the [ZnO(NO 3 ) 2 ] − complex produces several zinc-containing fragments. Three direct elimination products from [ZnO(NO 3 ) 2 ] − are identified as [Zn(NO 2 )(NO 3 )] − , [ZnO 2 (NO 3 )] − , and [ZnO(NO 3 )] − . The [ZnO 2 (NO 3 )] − product undergoes further elimination of O 2 to yield either [ZnO(NO 2 )] − or [Zn(NO 3 )] − . Theory predicts a mixture of the product isomers, [ZnO(NO 2 )] − and [Zn(NO 3 )] − , is formed due to similar energetics. The increased reactivity of [ZnO(NO 3 ) 2 ] − is attributed to radical anion character on the unique oxygen atom.

RATIONALE Polyethylene glycols (PEGs) are soluble molecules utilized in a wide range of applications. Mass spectrometry and fragmentation patterns of positively charged PEG oligomers are well-known, but decomposition mechanisms of the deprotonated ions have not been studied. METHODS Deprotonated PEGs were generated by electrospray ionization of PEG in water/acetonitrile. Collision-induced dissociation (CID) experiments were carried out in a tandem mass spectrometer. The anions were studied using a tandem mass spectrometer to carry out CID experiments. A series of small PEG oligomers, with 1 to 8 monomer units, were studied in order to monitor size-dependent effects on fragmentation reactions. RESULTS Because deprotonated PEG ions have a unique charge site, their dissociation pathways can easily be monitored. The ions fragment by loss of C2H4O monomer units, with an alternating intensity pattern that suggests the loss of an even number of monomer units is favored. Smaller oligomers and oligomer fragments also yielded fragments corresponding to H2 elimination and H2O loss. H2 elimination occurs by the generation of a hydride ion which deprotonates an alcohol upon leaving, while dehydration appears to be a charge-remote process. CONCLUSIONS The fragmentation of deprotonated PEG is dominated by intramolecular S(N)2 reactions involving the terminal oxide anion.

The manganese nitrate complex, [Mn(NO3)3](-), was generated via electrospray ionization and studied by tandem quadrupole mass spectrometry. The complex is assumed to decompose into [MnO(NO3)2](-) by elimination of NO2(•). The [MnO(NO3)2](-) product undergoes elimination of NO2(•) to yield [MnO2(NO3)](-), or elimination of NO(•) to yield [MnO3(NO3)](-). Both [MnO2(NO3)](-) and [MnO3(NO3)](-) yield [MnO4](-) via the transfer of oxygen atoms from the remaining nitrate ligand. The mechanism of permanganate formation is interesting because it can be generated through two competing pathways, and because the singlet ground state is spin-forbidden from the high-spin sextet [Mn(NO3)3](-) precursor. Theory and experiment suggest [MnO2(NO3)](-) is the major intermediate leading to formation of [MnO4](-). Theoretical studies show crossing from the high-spin to low-spin surface upon neutral oxygen atom transfer from the nitrate ligand in [MnO2(NO3)](-) allows formation of (1)[MnO4](-). Relative energy differences for the formation of (1)[MnO4](-) and (1)[MnO3](-) predicted by theory agree with experiment.

Negative ions of cyanoacetylene and cyanovinylidene are generated simultaneously via the competing 1,1-H(2)(+) and 1,2-H(2)(+) abstraction channels of O(-) reaction with acrylonitrile. The two stable isomeric forms of the anion, CCHCN(-) and HCCCN(-), are separated by a large (approximately 2 eV) potential energy barrier. Their photodetachment provides access to both the reactant and the product sides of the neutral cyanovinylidene --> cyanoacetylene rearrangement reaction, predicted to involve only a very small barrier. Using photoelectron imaging spectroscopy at 532 and 355 nm, the adiabatic electron affinity of the reactive intermediate :C horizontal lineCHCN (X(1)A'), is determined to be 1.84 +/- 0.01 eV. The photoelectron spectrum of CCHCN(-) exhibits a vibrational progression attributed to the excitation of the CCH bending mode. The observed spectral features are reproduced reasonably well using a Franck-Condon simulation under the parallel-mode approximation. In contrast to unsubstituted acetylene, cyanoacetylene has a stable anionic state, which is adiabatically weakly bound, but has an experimentally determined vertical detachment energy of 1.04 +/- 0.05 eV. This measurement, along with the broad, structureless photoelectron spectrum of HCCCN(-) (with no identifiable origin), reflects the large geometry difference between the w-shaped structure of the anion and the linear equilibrium geometry of HCCCN.

We present infrared photodissociation spectra of the microhydrated nitrate ions NO(3)(-)(H(2)O)(1-6), measured from 600 to 1800 cm(-1). The assignment of the spectra is aided by comparison with calculated B3LYP/aug-cc-pVDZ harmonic frequencies, as well as with higher-level calculations. The IR spectra are dominated by the antisymmetric stretching mode of NO(3)(-), which is doubly degenerate in the bare ion but splits into its two components for most microhydrated ions studied here due to asymmetric solvation of the nitrate core. However, for NO(3)(-)(H(2)O)(3), the spectrum reveals no lifting of this degeneracy, indicating an ion with a highly symmetric solvation shell. The first three water molecules bind in a bidentate fashion to the terminal oxygen atoms of the nitrate ion, keeping the planar symmetry. The onset of extensive water-water hydrogen bonding is observed starting with four water molecules and persists in the larger clusters.

The gas-phase vibrational spectroscopy of bare and monohydrated suberate dianions, (-)OOC-(CH(2))(6)-COO(-) and (-)OOC-(CH(2))(6)-COO(-).H(2)O, is studied by infrared photodissociation aided by electronic structure calculations. To this end, the corresponding ion-Kr atom complexes are formed in a cooled buffer-gas-filled ion trap, and their infrared vibrational predissociation spectra are measured in the range from 660 to 3600 cm(-1). The water molecule binds to one of the two carboxylate groups in a bidentate fashion, characterized by the splitting of the carboxylate stretching bands, a substantially blue-shifted water bending band, and the presence of anomalously broadened bands in the O-H stretching and H(2)O rocking region. The C-C backbone structure remains unperturbed by the addition of a water molecule or a Kr atom. At 63 K, the all-trans isomer is the most abundant species, but evidence for dynamically interconverting conformers is also present from contributions to the absorption cross section on the low-energy tail of the C-H stretching region.

We have studied the protonated ether-(H2O)n (n = 1-3) complexes containing tetrahydrofuran, dimethyl, diethyl, dibutyl, and butylmethyl ethers using a flowing afterglow triple-quadrupole mass spectrometer. Collision-induced dissociation, CID, of all clusters with n = 1, 2 shows sequential water loss. The n = 3 cluster of dimethyl ether shows sequential water loss, while all other ether clusters display selective product formation. The CID spectra are interpreted based on known energetics, and theoretical studies of the dimethyl and diethyl ether systems.

Building on the past studies of the O2n− and O2−(H2O)m cluster anion series, we assess the effect of the strong hydration interactions on the oxygen-core clusters using photoelectron imaging and photofragment mass spectroscopy of [O2n(H2O)m]− (n=1–4, m=0–3) at 355 nm. The results show that both pure-oxygen and hydrated clusters with n≥2 form an O4− core anion, indicated in the past work on the pure-oxygen clusters. All clusters studied can be therefore described in terms of O4−(H2O)m(O2)n−2 structures, although the O4− core may be strongly perturbed by hydration in some of these clusters. Fragmentation of these clusters yields predominantly O2− and O2−(H2O)l (l

A novel instrumental setup for measuring infrared photodissociation spectra of buffer gas cooled, mass‐selected ions is described and tested. It combines a cryogenically cooled, linear radio frequency ion trap with a tandem mass spectrometer, optimally coupling continuous ion sources to pulsed laser experiments. The use of six independently adjustable DC potentials superimposed over the trapping radio frequency field provides control over the ion distribution within, as well as the kinetic energy distribution of the ions extracted from the ion trap. The scheme allows focusing the ions in space and time, such that they can be optimally irradiated by a pulsed, widely tunable infrared photodissociation laser. Ion intensities are monitored with a time‐of‐flight mass spectrometer mounted orthogonally to the ion trap axis.