R. S. Walters

Infrared spectroscopy of V+(H2O) and V+(D2O) complexes: Solvent deformation and an incipient reaction

V+(H2O)Arn and V+(D2O)Arn complexes are studied with mass-selected infrared photodissociation spectroscopy in the O–H (O–D) stretch region. Two vibrational bands are measured 50–80 cm−1 to the red from the symmetric and asymmetric stretches in free water. Rotational analysis for V+(H2O)Ar indicates a C2v geometry with argon opposite water and significant expansion of the H–O–H angle. The v=1 level in the asymmetric stretch undergoes distortion consistent with selective excitation into the coordinate of an insertion reaction.

Frontiers in the infrared spectroscopy of gas phase metal ion complexes

Studies of gas phase M+(L)n cluster ions (where M is a metal atom and L is a ligand molecule) assist our understanding of solvation and chemical processes that involve metal ions. The recent development of pulsed, tuneable OPO (optical parametric oscillator) sources capable of generating infrared light at frequencies between 1000 and 4000 cm−1 has allowed the vibrational spectra of many species to be assigned for the first time. This perspective reviews infrared spectroscopy of metal-containing cluster ions to date and discusses future opportunities.

Infrared photodissociation spectroscopy of V+(CO2)n and V+(CO2)nAr complexes

V+(CO2)n and V+(CO2)nAr complexes are generated by laser vaporization in a pulsed supersonic expansion. The complexes are mass-selected within a reflectron time-of-flight mass spectrometer and studied by infrared resonance-enhanced (IR-REPD) photodissociation spectroscopy. Photofragmentation proceeds exclusively through loss of intact CO2 molecules from V+(CO2)n complexes or by elimination of Ar from V+(CO2)nAr mixed complexes. Vibrational resonances are identified and assigned in the region of the asymmetric stretch of free CO2 at 2349 cm(-1). A linear geometry is confirmed for V+(CO2). Small complexes have resonances that are blueshifted from the asymmetric stretch of free CO2, consistent with structures in which all ligands are bound directly to the metal ion. Fragmentation of the larger clusters terminates at the size of n=4, and a new vibrational band at 2350 cm(-1) assigned to external ligands is observed for V+(CO2)5 and larger cluster sizes. These combined observations indicate that the coordination number for CO2 molecules around V+ is exactly four. Fourfold coordination contrasts with that seen in condensed phase complexes, where a coordination number of six is typical for V+. The spectra of larger complexes provide evidence for an intracluster insertion reaction that produces a metal oxide-carbonyl species.

Infrared Spectroscopy of Solvation and Isomers in Fe + (H2O)1,2Arm Complexes

Vibrational spectroscopy in the OH-stretching region is reported for the mass-selected ion–molecule complexes Fe+(H2O)Ar2 and Fe+(H2O)2Ar. These species are produced by laser vaporization in a pulsed nozzle cluster source, mass-selected with a reflectron time-of-flight mass spectrometer, and studied with infrared laser photodissociation spectroscopy. To achieve efficient photodissociation, the pure metal–water complexes are ‘tagged’ with weakly bound argon atoms. Such tagging is expected to exert a minor perturbation on the spectroscopy. However, we find that this may not be true depending on the binding site. The symmetric stretch and asymmetric stretch of water in these complexes shifts 30–50 cm−1 to the red as a result of binding to the metal cation, and an additional redshift is found for isomers with argon bound to the OH of water. The relationships between isomers and infrared spectra are discussed.

Generation of "unstable" doubly charged metal ion complexes in a laser vaporization cluster source

Doubly charged metal ion complexes of the form M 2+ (L)n are generated using a laser vaporization cluster source in conjunction with a time-of-flight mass spectrometer. Contrary to expectations, a variety of doubly charged species are produced with this source, including many so-called “unstable” or “metastable” ions in which the metal has a second ionization potential greater than the first ionization potential of the ligand or solvent. The species identified include Mg 2+ (CO2)n ,M g 2+ (H2O), Mg 2+ (Ar)n ,C o 2+ (Ar)n ,C o 2+ (H2O), Si 2+ (Ar)n and Ti 2+ (CO2)n. This is apparently the first observation by any means of Co 2+ (Ar)n ,T i 2+ (CO2)n and Si 2+ (Ar)n. Of the complexes studied, only the “stable” species Mg 2+ (Ar)n have been generated previously by laser vaporization. The conditions necessary for the production of these ions are investigated and possible mechanisms for their growth are suggested. Charge-transfer photodissociation is observed for Co 2+ (Ar) complexes.

Growth dynamics and intracluster reactions in Ni+(CO2)n complexes via infrared spectroscopy

Ni(+)(CO(2))(n), Ni(+)(CO(2))(n)Ar, Ni(+)(CO(2))(n)Ne, and Ni(+)(O(2))(CO(2))(n) complexes are generated by laser vaporization in a pulsed supersonic expansion. The complexes are mass-selected in a reflectron time-of-flight mass spectrometer and studied by infrared resonance-enhanced photodissociation (IR-REPD) spectroscopy. Photofragmentation proceeds exclusively through the loss of intact CO(2) molecules from Ni(+)(CO(2))(n) and Ni(+)(O(2))(CO(2))(n) complexes, and by elimination of the noble gas atom from Ni(+)(CO(2))(n)Ar and Ni(+)(CO(2))(n)Ne. Vibrational resonances are identified and assigned in the region of the asymmetric stretch of CO(2). Small complexes have resonances that are blueshifted from the asymmetric stretch of free CO(2), consistent with structures having linear Ni(+)-O=C=O configurations. Fragmentation of larger Ni(+)(CO(2))(n) clusters terminates at the size of n=4, and new vibrational bands assigned to external ligands are observed for n> or =5. These combined observations indicate that the coordination number for CO(2) molecules around Ni(+) is exactly four. Trends in the loss channels and spectra of Ni(+)(O(2))(CO(2))(n) clusters suggest that each oxygen atom occupies a different coordination site around a four-coordinate metal ion in these complexes. The spectra of larger Ni(+)(CO(2))(n) clusters provide evidence for an intracluster insertion reaction assisted by solvation, producing a metal oxide-carbonyl species as the reaction product.

Growth dynamics and intracluster reactions in Ni{sup +}(CO{sub 2}){sub n} complexes via infrared spectroscopy

Ni(+)(CO(2))(n), Ni(+)(CO(2))(n)Ar, Ni(+)(CO(2))(n)Ne, and Ni(+)(O(2))(CO(2))(n) complexes are generated by laser vaporization in a pulsed supersonic expansion. The complexes are mass-selected in a reflectron time-of-flight mass spectrometer and studied by infrared resonance-enhanced photodissociation (IR-REPD) spectroscopy. Photofragmentation proceeds exclusively through the loss of intact CO(2) molecules from Ni(+)(CO(2))(n) and Ni(+)(O(2))(CO(2))(n) complexes, and by elimination of the noble gas atom from Ni(+)(CO(2))(n)Ar and Ni(+)(CO(2))(n)Ne. Vibrational resonances are identified and assigned in the region of the asymmetric stretch of CO(2). Small complexes have resonances that are blueshifted from the asymmetric stretch of free CO(2), consistent with structures having linear Ni(+)-O=C=O configurations. Fragmentation of larger Ni(+)(CO(2))(n) clusters terminates at the size of n=4, and new vibrational bands assigned to external ligands are observed for n> or =5. These combined observations indicate that the coordination number for CO(2) molecules around Ni(+) is exactly four. Trends in the loss channels and spectra of Ni(+)(O(2))(CO(2))(n) clusters suggest that each oxygen atom occupies a different coordination site around a four-coordinate metal ion in these complexes. The spectra of larger Ni(+)(CO(2))(n) clusters provide evidence for an intracluster insertion reaction assisted by solvation, producing a metal oxide-carbonyl species as the reaction product.

Growth Dynamics and Intracluster Reactions in Ni + (CO 2 ) n via infrared spectroscopy

Ni(+)(CO(2))(n), Ni(+)(CO(2))(n)Ar, Ni(+)(CO(2))(n)Ne, and Ni(+)(O(2))(CO(2))(n) complexes are generated by laser vaporization in a pulsed supersonic expansion. The complexes are mass-selected in a reflectron time-of-flight mass spectrometer and studied by infrared resonance-enhanced photodissociation (IR-REPD) spectroscopy. Photofragmentation proceeds exclusively through the loss of intact CO(2) molecules from Ni(+)(CO(2))(n) and Ni(+)(O(2))(CO(2))(n) complexes, and by elimination of the noble gas atom from Ni(+)(CO(2))(n)Ar and Ni(+)(CO(2))(n)Ne. Vibrational resonances are identified and assigned in the region of the asymmetric stretch of CO(2). Small complexes have resonances that are blueshifted from the asymmetric stretch of free CO(2), consistent with structures having linear Ni(+)-O=C=O configurations. Fragmentation of larger Ni(+)(CO(2))(n) clusters terminates at the size of n=4, and new vibrational bands assigned to external ligands are observed for n> or =5. These combined observations indicate that the coordination number for CO(2) molecules around Ni(+) is exactly four. Trends in the loss channels and spectra of Ni(+)(O(2))(CO(2))(n) clusters suggest that each oxygen atom occupies a different coordination site around a four-coordinate metal ion in these complexes. The spectra of larger Ni(+)(CO(2))(n) clusters provide evidence for an intracluster insertion reaction assisted by solvation, producing a metal oxide-carbonyl species as the reaction product.