D. L. Robbins

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...

Electronic spectroscopy of the Mg+–N2 complex: Evidence for photoinduced activation of N2

The ion–molecule complex, Mg+–N2 is formed in a supersonic expansion and studied with mass‐selected photodissociation spectroscopy. The lowest energy bands observed in the electronic excitation spectrum are redshifted more than 12 000 cm−1 from the Mg+ (2P←2S) atomic transition at 280 nm. The red‐shift, resulting from differential bonding in the ground and excited states of the complex, is much larger than the shifts observed in previously studied Mg+–ligand complexes. Resolved vibronic structure is observed extending for more than 5000 cm−1. The observation of spin–orbit multiplet structure indicates that the complex is linear and that the electronic transition is 2Π←X 2Σ+. The spin–orbit splitting of 46 cm−1 is significantly less than that observed for other Mg+–L complexes. Vibronic intervals of about 1000 and 500 cm−1 are assigned respectively to a stretching mode and to double quanta in a bending mode. The study of isotopically substituted complexes indicates that the best assignment for the stretch ...

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.

Photoionization electronic spectroscopy of AlOH

Abstract An electronic spectrum is observed for AlOH formed in a laser vaporization pulsed molecular beam source. The spectrum is detected near 250 nm by resonant two-photon ionization spectroscopy. Two electronic states are observed, spaced by only 1674 cm −1 . Vibrational progressions are observed in both states corresponding to the excited state AlOH stretching mode (ω′ e = 825 cm −1 ) and the AlOH bending mode (ω′ e = 654 cm −1 ). The spectrum is consistent with a quasi-linear ground state and a more strongly bent excited state, as predicted by theory.

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 ...

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.

A convenient modification to the Newport pulsed molecular‐beam valve

We describe a modification to Newport Corporation’s BV‐100 double solenoid pulsed molecular‐beam valve that replaces the Viton tip seal with an O‐ring‐based plug. This alteration produces the same characteristic short and cold gas pulses as the originally described beam valve without the difficulties associated with replacing the seal.

Photoionization electronic spectroscopy of AlAg

AlAg is produced in a supersonic molecular beam by laser vaporization of alloy samples in a pulsed nozzle cluster source. Electronic spectroscopy is studied with resonant two‐photon photoionization. In addition to the two electronic excited states previously reported by Clements and Barrow, we have observed ten new states. Vibrational analyses are presented for each of these states, and rotational analyses are given for selected states. The number and characteristics of these excited states are compared to the predictions of recent ab initio calculations.