Michel Heninger

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.

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.

MICRA: a compact permanent magnet Fourier transform ion cyclotron resonance mass spectrometer.

MICRA,1 a compact Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer is described. The amount of miniaturisation in this device, based on a 1.24 T permanent magnet, remains compatible with genuine FT-ICR performance and analytical power in the mass range 2–1000 m/z, with a mass resolving power of 73,000 at mass 132. A first application of the transportability is the repetitive coupling of MICRA with a large-scale source of IR photons, the free electron laser CLIO.

Comparison of energy partitioning in Ar+ and N2+ charge-transfer reactions

The kinetic energy released in near-thermal charge-transfer reactions of Ar+ and N2+ with NO, O2, CO, H2O, N2O, CO2 and NH3 has been measured. The partitioning between kinetic and internal modes is found to be very similar for most of the Ar+/N2+ pairs. Two hypotheses to explain this similarity are proposed and discussed.

Radiative relaxation of NO+ (X, v = 1−4)

Abstract Radiative lifetimes of NO + (X, v =1–4) has been determined using the monitor ion technique in a triple cell ICR spectrometer with Fourier transform detection. Correction of the measured lifetimes for radiative cascades and quenching is discussed in detail. The corrected lifetimes are in very good agreement with the best available theoretical data.

Detailed Characterization of 2-Heptanone Conversion by Dielectric Barrier Discharge in N2 and N2/O2 Mixtures

The products of 2-heptanone conversion by dielectric barrier discharge plasma are analyzed under different conditions: alternating current (ac) or pulsed mode of excitation, variable energy, variable composition of the carrier gas. The efficiency of the conversion is higher using a pulse excitation mode than an ac mode. With a small oxygen percentage (about 2-3%) added to nitrogen, 2-heptanone is about 30% more efficiently removed than in pure nitrogen, while the 2-heptanone removal decreases with an oxygen percentage higher than 3%. A new analysis method, based on chemical ionization mass spectrometry, is used for volatile organic compound detection along with chromatography. Several products issued from 2-heptanone conversion with ac excitation are identified in nitrogen and in air, and a chemical scheme is proposed to explain their formation and their treatment by the discharge. It appears that byproducts are issued not only from oxidation reactions, but also from C-C bond cleavage by collisions with electrons or nitrogen excited states.

Radiative relaxation of vibrationally excited ions

Abstract A triple cell ICR spectrometer analogous to a three-stage mass spectrometer (MS/MS/MS) but capable of studying thermal energy collisions is described. The facility to store ions in a good vacuum allows the measurement of radiative lifetimes using a chemical reaction to probe the energy contents of the ions as a function of their storage time. Vibrational lifetimes have been measured for two diatomic ions in their electronic ground state: NO+ and HCl+. NO+ and NO have similar lifetimes, in very good agreement with calculated values. HCl+ (v = 1) has a lifetime ten times shorter than HCl (3 ± 1 ms compared with 29 ms), in fairly good agreement with the calculated value of 4.6 ms. This is the first experimental confirmation of the very short lifetimes predicted theoretically for diatomic hydride ions. Qualitative results have been obtained for the radiative lifetime of NH3+. The shape of the decay curves indicates the presence of long-lived (more than 300 ms) and short-lived (10–20 ms) states.

Successive reactions of iron carbonyl cations with dimethyl ether: direct cleavage versus rearrangement

The reaction kinetics of electron impact ionization generated Fe(CO)n+ cations with dimethyl ether (DME) is investigated using a triple-cell Fourier Transform Ion Cyclotron Resonance spectrometer. The primary reaction is rapid substitution of CO by DME. One-step substitution of two CO ligands by one DME molecule also occurs for n = 3–4, and for unrelaxed Fe(CO)2+ ions. Successive substitutions in the Fe(CO)4+/DME system lead mainly to Fe(CO)(DME)2+, in which the last CO remains unsubstituted. This ion is slowly converted to Fe(CO)(DME)3+ and Fe(DME)2+. The latter reaction implies formation of neutral CH3COOCH3 resulting from iron-promoted CO insertion reaction. Further reaction of Fe(DME)+ with DME involves the cleavage of a C–O bond according to two channels, either direct CH3˙ loss or more exothermic CH4 loss, implying a molecular rearrangement. The branching ratio is strongly energy-dependent: the latter channel is observed only for Fe(DME)+ ions having a very low energy content.

Experimental investigation of vibrational radiative lifetimes: H2O+ and D2O+ ions in their ground electronic state (X 2B1)

Radiative lifetimes of vibrationally excited H2O+ and D2O+ ions in their ground electronic state (X 2B1) have been determined using the monitor ion technique in a triple cell ion cyclotron resonance spectrometer with Fourier transform detection. The monitor reactions are proton or deuteron transfer from H(D)2O+ to CO2 and N2O. The lifetimes are corrected for collisional deactivation and reactions with the background gases occurring during the relaxation time of the ions. N2O probes all the excited vibrational levels of H2O+ and D2O+. For H2O+ only the bending modes (0,v≥1,0) contribute to the decay curve. The corresponding overall lifetime, 26.8±3 ms, is in very good agreement with the computer simulated overall lifetime including the theoretical lifetimes of Weis et al. [J. Chem. Phys. 91, 2818 (1989)] and estimated populations of the bending vibrational levels. For D2O+, the overall lifetime of the (0,v≥1,0) bending modes, 99.5±15 ms, and the lifetime of the (1,0,0) stretching mode, 27.5±4.5 ms, are obs...

On the lifetime of electronically excited acetone molecular ions

Abstract A triple-cell ICR spectrometer has been used to study the dissociation of electronically excited acetone ions (CH 3 ) 2 CO +* induced by collision with He and to measure their radiative lifetime. The threshold energy for CID is around 0.15 eV, consistent with a small barrier to curve-crossing into the ground state from which dissociation occurs. Endothermic charge transfer with O 2 has also been used to probe the internal energy of acetone ions as a function of storage time. The radiative lifetime depends on the internal energy of the ions: 4 +2 −1 and 14 ± 3 ms, determined respectively by CID with He and charge transfer with O 2 , corresponding to E int ⩾ 2.9 eV and E int ⩾ 2.4 eV.