G. Mauclaire

Ultrasensitive spectroscopy of ionic reactive intermediates in the gas phase performed with the first coupling of an IR FEL with an FTICR-MS

First example of coupling a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FTICR-MS) with an infrared Free Electron Laser (FEL) is presented. This experimental setup is ideally suited for the direct structural characterization of reactive polyatomic ions. Ultrasensitive measurements of the infrared vibrational spectrum of ionic reactive intermediate selectively prepared is allowed by the association of the high peak power of the FEL, its wide tunability, and the flexibility of FTICR-MS, where several mass selections and ion-molecule reactions can be combined. These possibilities are demonstrated in the case of Fe + complexes where two photofragmentation pathways compete. The resulting infrared spectrum is in excellent agreement, both with respect to the position and to the relative intensities of the infrared transitions, with predicted by ab initio electronic structure calculations. r 2003 Elsevier Science B.V. All rights reserved.

Energy disposal in thermal‐energy charge transfer reactions determined by kinetic energy measurements of product ions: Ne++O2→O++O+Ne and Ar++O2→O2++Ar

The possibility of deducing reaction mechanisms from kinetic energy released in the products is discussed for thermal energy ion‐molecule reactions. An experimental method based on ICR spectrometry is described, allowing for the first time kinetic energy measurements of ions produced in thermal energy reactions. Application to charge transfer from Ne+ and Ar+ to O2 is presented. Ne+ produces O+ ions with 0.55 eV mean KE, corresponding to the O+(4S°)+O(1D) dissociation limit of O2+, while Ar+ produces O2+ molecular ions with 1 eV mean KE corresponding to ground state ions in rather high vibrational states (?∼8–10). With Ne+ the results can be accounted for in the framework of a (quasi) resonant charge transfer process while with Ar+ charge transfer involves electronic into kinetic energy transfer.

Luminescence in near-thermal charge exchange, I: He++N2

Abstract A pulsed Ion Cyclotron Resonance cell fitted with synchronous photon-counting equipment is used to study the emission produced by near-thermal (≲0.1

Radiative lifetime for v = 1 and v = 2 ground state NO+ ions

Abstract Radiative lifetimes of vibrationally excited ions in their electronic ground state have been measured for the first time. A nonoptical technique has been developed, involving ion cyclotron resonance trapping in conjunction with chemical monitoring of the energy content of the ions. For NO + (X 1 Σ + ) ions, the measured lifetimes of 95 ± 15 ms for v = 1 and 46 ± 10 ms for v = 2 are in excellent agreement with the values obtained from the ab initio calculations of Werner and Rosmus.

Thermal-energy charge transfer of Ar+ with H2O: Internal and kinetic energy of the product H2O+

Abstract The reaction of Ar + with H 2 O has been investigated at near-thermal energy. The product ions H 2 O + and ArH + account for 90 and 10% of the total reaction rate, respectively. Kinetic energy measurements and emission spectroscopy of the H 2 O + product ions are reported. It is concluded that at least 60% of H 2 O + ions are in the X state with ≈2.4 eV vibrational energy while up to 40% are in the A state with a mean vibrational energy of 1.4 eV; the A state vibrational distribution has been determined. It is shown that both H 2 O + states are populated via an energetically “non-resonant” charge transfer process.

Thermal energy charge transfer from He+ to O2 : Kinetic energy, nature, and reactivity of the O+ product ions

From kinetic energy measurements in an ICR cell, the charge‐transfer reaction between thermal He+ and O2 is shown to produce 64% of ground state O+ ions with 1.8 eV kinetic energy, and 36% of electronically excited O+* with 0.3 eV kinetic energy. These O+* react with O2 with a rate constant of 6.5×10−10 cm3s−1. The nature of this excited state, 2D° or 2P°, is discussed. A resonant, long‐distance electron jump explains all the experimental data.

Negative ion reactions in N2O at low energies

The reaction of O− with N2O has been studied as a function of temperature and O− kinetic energy using ion cyclotron resonance and flowing afterglow techniques. The reaction has a measured rate constant at room temperature of 2.2± 0.4 cm3/sec in the flowing afterglow and 2.5± 0.5 × 10−10cm3/sec in the ICR. As the O− energy is increased the rate constant declines. Over the entire range of energies NO− is the only observed reaction product. Energy exchange between O− and N2O and Ar have also been studied as well as reactions involving the NO− product of the O− reaction with N2O. The present results are compared with previous results.

Laser induced fluorescence of ions trapped in an ion cyclotron resonance cell: Excitation of CO+X 2Σ, v′′ = 0 and relaxation of CO+A 2Π, v′ = 1

An experimental setup has been designed to study laser induced fluorescence of ions produced and trapped in an ICR cell. Fluorescence excited by a tunable dye laser and spontaneous emission may be observed. Production, trapping, excitation, and observation are pulsed and a time resolved signal processing is used in order to identify the different excited species and measure their lifetime. Excitation spectra of CO+A 2Π, v′ = 1←X 2Σ, v\ = 0 in pure CO and (Ar,CO) mixtures are presented. A radiative lifetime τR = 3.5 μs and collisional quenching rates kQ = 7.5×10−10 cm3 molecule−1 s−1 in CO and k′Q = 5.9×10−10 cm3 molecule−1 s−1 in Ar have been determined for the v′ = 1 level of the CO+A 2Π1/2 state.

Energy partitionning in charge transfer reactions at thermal energies

Abstract Non dissociative charge transfer reactions from Ar + , Kr + , Xe + , N 2 + , CO + , O 2 + and CO 2 + to several small molecules have been investigated at near thermal collision energies. In most cases a substantial amount (up to 1.8 eV) of kinetic energy release is measured. In C.T. from atomic ions the internal energy of the product molecular ion(M + ) is then deduced from energy balance and it turns out that M + is usually formed in high vibrational levels of the ground electronic state with a rather narrow vibrational distribution. Partitioning between internal and kinetic energy of M + is correlated to its size. In C.T. from molecular ions(P + ) complementary experiments have to be performed to determine separately the internal energy of the neutral (P) and ionic (M + ) products.

Energy disposal in thermal-energy charge-transfer reactions: Ar+,Kr+ and Xe+ with NH3

Abstract Thermal-energy charge-transfer reactions from the 2 P 3/2 state of Ar + , Kr + and Xe + with NH 3 are shown to be non-energy resonant: the kinetic energy released in each case has been measured, and the internal energy of the NH + 3 product ions deduced. Possible quenching of 2 P 1/2 state of rare-gas ions in ICR cells is discussed.