K. F. Willey

Reflectron time‐of‐flight mass spectrometer for laser photodissociation

We describe a new reflectron time‐of‐flight mass spectrometer configuration for laser photodissociation of mass‐selected ions and the initial performance characteristics observed for this instrument. Ions are produced by laser photoionization within the acceleration region of the instrument or by laser vaporization in an external pulsed‐nozzle cluster ion source. Mass selection is accomplished with pulsed deflection plates at the end of an initial drift section. Laser photodissociation of selected ions takes place at the turning point in the ion trajectory in the reflectron. The transit time through a second drift section defines the fragment ion masses. Optimized operating conditions and the role of mass discrimination in this instrument are discussed.

Photodissociation spectroscopy of Mg+–H2O and Mg+–D2O

Mg+–H2O ion–molecule complexes are produced in a pulsed supersonic nozzle cluster source. These complexes are mass selected and studied with laser photodissociation spectroscopy in a reflectron time‐of‐flight mass spectrometer system. An electronic transition assigned as 2B2←X 2A1 is observed with an origin at 28 396 cm−1. The spectrum has a prominent progression in the metal‐H2O stretching mode with a frequency (ω’e) of 518.0 cm−1. An extrapolation of this progression fixes the excited state dissociation energy (D’0) at 15 787 cm−1. The corresponding ground state value (D‘0) is 8514 cm−1 (24.3 kcal/mol). The solvated bending mode, and symmetric and asymmetric stretching modes of water are also active in the complex, as are the magnesium bending modes. A second electronic transition assigned as 2B1←X 2A1 is observed with an origin at 30 267 cm−1 and a metal stretch frequency for Mg+–H2O of 488.5 cm−1 (ΔG1/2). Spectra of both excited states are also observed for Mg+–D2O. Partially resolved rotational struc...

Photodissociation spectroscopy of the Mg+-CO2 complex and its isotopic analogs

Mg+–CO2 ion–molecule cluster complexes are produced by laser vaporization in a pulsed nozzle cluster source. The vibronic spectroscopy in these complexes is studied with mass‐selected photodissociation spectroscopy in a reflectron time‐of‐flight mass spectrometer. Two excited electronic states are observed (2) 2Σ+ and 2Π. The 2Π state has a vibrational progression in the metal–CO2 stretching mode (ωe’=381.8 cm−1). The complexes are linear (Mg+–OCO) and are bound by the charge–quadrupole interaction. The dissociation energy (D0‘) is 14.7 kcal/mol. Corresponding spectra are measured for each of the 24, 25, and 26 isotopes of magnesium. These results are compared to theoretical predictions made by Bauschlicher and co‐workers.

Spectroscopy of weakly-bound magnesium ion complexes

Abstract Weakly bound complexes of the form Mg+-L (L = CO2 , H2O, N2, Ar, etc.) are prepared in a pulsed nozzle/laser vapourization cluster source and studied in the molecular beam environment. The ion complexes are jet cooled and mass selected in a specially designed reflectron time-of-flight mass spectrometer for their study. The mass-selected ions are excited with a tunable dye laser, and the products, if any, from photodissociation are mass analysed and detected as a function of the excitation laser wavelength. This photodissociation spectroscopy experiment reveals the decomposition channels of excited complexes and their absorption spectra. Photodissociation channels vary from simple metal ion-ligand bond breaking, to metal-to-ligand charge transfer, to metal insertion/elimination reactions in the excited state. In reactive systems, the spectra are broad and featureless. However, in systems with simple metal—ligand dissociation, vibrational and partial rotational resolution is obtained in the spectra...

Mass-analyzed threshold ionization spectroscopy of AlAr

Abstract Mass-analyzed threshold ionization (MATI) spectroscopy is applied for the first time to a metal van der Waals complex, AlAr. The experimental configuration for MATI uses a time-of-flight mass spectrometer, oriented perpendicular to the molecular beam axis, without modification of any components. The vibrationally resolved spectrum yields a frequency of ω″ e =67 cm −1 for the ground state of Al + Ar, and a value of Δ G ″ 1 2 =39 cm −1 for neutral AlAr.

Photodissociation of magnesium ion/molecule complexes in a reflectron time-of-flight mass spectrometer

Abstract Ion/molecule cluster complexes containing magnesium (e.g., Mg + −(CO 2 ) x , Mg + −(H s O) x ) are generated in a pulsed nozzle cluster source. Specific ions are size selected from the source distribution with a reflectron time-of-flight mass spectrometer for studies of their photodissociation dynamics. Photoexcitation of these complexes near the Mg + ( 2 S→ 2 P) resonance line causes a variety of novel photochemistry, ranging from simple ligand ejection, to metal insertion, to metal-ligand charge exchange. These reactions are first observed in the single molecule complexes, and they persist in larger aggregates with more extensive solvation. Excitation spectra probe the energy dependence of the photochemistry and they provide information on the structures of the ion/molecule complexes.

Electronic spectroscopy of silver dimer rare gas complexes

Vibrationally resolved electronic spectra are reported for the metal dimer‐rare gas complexes Ag2–Ar and Ag2–Kr. These spectra are obtained using resonant two‐photon photoionization in the energy region near the Ag2 B←X electronic transition (280–285 nm). Both complexes exhibit extensive activity in three vibrational modes, making it possible to determine vibrational constants, anharmonicities, and cross‐mode couplings. An unusual cancellation of factors results in the Kr complex (ω’e =72.6 cm−1) having nearly the same metal‐rare gas stretching frequency as the Ar complex (ωe=73.9 cm−1). Progressions extending over a significant range of the excited state potential surfaces make it possible to derive the excited state dissociation energies (D’0=755 and 1205 cm−1 for Ar and Kr, respectively). Combination with the red‐shifted electronic state origins yields the corresponding ground state dissociation energies (D■0=275 and 394 cm−1 for Ar and Kr, respectively). Potential energy surfaces are investigated for ...

On the assignment of Jahn–Teller effects in the ultraviolet absorption spectrum of Ag3

A Jahn–Teller linear‐plus‐quadratic Hamiltonian is shown to account for most of the observed band positions and intensities in the absorption and emission spectra of Ag3. Coupling parameters obtained for a simultaneous fit to absorption and emission results are k=1.93, g=0.25 for the E’ ground state and k=0.19, g=0.02 for the E‘ excited state. At higher vibrational energies, simple Jahn–Teller calculations predict fewer bands than observed. Calculations including spin–orbit coupling with larger linear coupling partially quenched by the Ham effect offer a reasonable explanation for this higher energy structure. Splittings and intensity sharing at lower vibrational energies, however, demand higher‐order Jahn–Teller coupling, indicating the need for more extensive calculation simultaneously incorporating quadratic Jahn–Teller effects, spin–orbit coupling, and perhaps anharmonicity.

Photodissociation spectroscopy of Mg+H2O

Mg+H2O ion—molecule complexes are produced in a pulsed supersonic nozzle cluster source. These weakly bound complexes are mass selected and studied with laser photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer system. An electronic transition assigned as 2B2→X2A1 is observed with an origin at 28399 cm−1 (vac). The spectrum has a prominent progression in the metal—H2O stretching mode with a frequency (ω′e) of 517.1 cm−1. An extrapolation of this progression fixes the excited state dissociation energy (D′0) at 16008 cm−1. The corresponding ground state value (D″0) is 8732 cm−1 (25.0 kcal/mol). The solvated bending mode and asymmetric stretching mode of water are also active in the complex. A second electronic transition assigned as 2B1←X 2A1 is observed with an origin at 30386 cm−1 and a metal stretch frequency of 483.4 cm−1. This study was guided by ab initio calculations by Bauschlicher and co-workers, which provide accurate predictions of the electronic transition energies, vibrational constants and dissociation energies.

Vibronic spectroscopy of Ag2-Ar

Abstract The weakly bound complex Ag 2 -Ar is produced using laser vaporization of solid silver in a pulsed supersonic molecular beam. Resonant two-photon photoionization yields a vibrationally-resolved electronic spectrum with an origin at 35329 cm −1 . This origin is red-shifted 480 cm −1 from that of the uncomplexed silver dimer. Progressions are observed for the solvated Ag 2 stretch (156 cm −1 ), the van der Waals stretch (74 cm −1 ) and the bending mode (28 cm −1 ). Excited state (755 cm −1 ) and ground state (275 cm −1 ) binding energies are obtained.