Correlated detection of neutral and charged fragments in collision induced fragmentation of molecular clusters

accepté dans International Journal of Mass SpectrometryWe report on collision induced fragmentation of isolated molecular nanosystems studied with an event by event detection technique including the correlated detection of both neutral and charged fragments. This work focuses on the dissociation induced by collisional excitation without ionisation and electron-capture. Two molecular cluster cations are investigated: the collision of protonated hydrogen clusters at 60keV/amu with helium targets and that of protonated water clusters at 8keV with an argon gas. In addition to the molecular evaporation process the dissociation channel leading to the production of the H3+ or H3O+ molecular cations (loss of all the molecules) is observed with an unexpected abundance. The cross section for the production of these cations is observed to increase with the number of molecules in the cluster. Such an increase cannot be associated with the direct collisional excitation of the cation core of the cluster

Probing the liquid-t-gas like phase transition in a cluster via a caloric curve

IP

Total partial and electron-capture cross sections for ionization of water vapor by 20-150 keV protons

IP

Charge-Transfer Induced Dissociation in the H+(H2O)3-Ar collisions observed with the COINTOF mass spectrometer

Electron-capture in collisions of singly charged protonated water cluster H+(H2O)3, ions with Ar atoms is studied at the impact energy of 8 keV in the frame of the COrrelated Ion and Neutral fragments Time-Of-Flight, COINTOF, technique. In contrast to methods based only on the detection of the charged fragments, dissociation induced by collisional-excitation and electron-capture induced dissociation can be simultaneously recorded in the present set-up. Time of flight measurement of both neutral and corresponding charged species resulting from the charge-exchange process leads to the direct observation of the dissociation of the neutralized protonated water cluster. Thus, the present COINTOF method provides new valuable insights into the collision processes through the detection of produced neutral fragments. Moreover, it opens new possibilities to measure kinetic energy release also in the dissociation of the produced neutrals, which is our future endeavour in the development of the presented COINTOF set up

Reply to the comment on direct experimental evidence for a negative heat capacity in the liquid to gas phase transition in hydrogen cluster ions backbending of the caloric curve

IP

Collision induced cluster fragmentation: From fragment size distributions to the caloric curve

IPMInternational audienceWe report on a cluster fragmentation study involving collisions of high-energy (60 keV/amu) H3+(H2)m hydrogen cluster ions (m=9, 11) with atomic helium or fullerenes. The experimental characterisation of the cluster fragmentation not only by the average fragment size distribution but also by a statistical analysis of the fragmentation events has become possible owing to a recently developed multi-coincidence technique in which all the fragments of all collisions occurring in the experiment are mass analysed on an event-by-event basis. By selecting specific decay reactions we can start after the energizing collision with a microcanonical cluster ion ensemble of fixed excitation energy. From the respective fragment distributions for these selected decay reactions we derive corresponding temperatures of the decaying cluster ions. The relation between this temperature and the excitation energy (caloric curve) exhibits the typical prerequisites of a first order phase transition in a finite system, in the present case signalling the transition from a bound cluster type situation to the free gas phase

A novel "Correlated Ion and Neutral Time Of Flight" Method: event-by-event detection of neutral and charged fragments in Collision Induced Dissociation (CID) of mass selected ions

accepté dans Rev. Sci. Instrum.A new mass spectrometric MS-MS method based on Time Of Fight measurements performed on an event-by-event detection technique is presented. This "COrrelated Ion and Neutral Time of Flight (COINTOF)" method allows to explore CID fragmentation processes by directly identifying not only all ions and neutral fragments produced but also their arrival time correlations within each single fragmentation event from a dissociating molecular ion. This constitutes a new step in the characterization of molecular ions. The method will be illustrated here for a prototypical case involving Collision Induced Dissociation (CID) of protonated water clusters H+(H2O)n=1-5 upon collisions with argon atoms

Electron-loss and target ionization cross sections for water vapor by 20-150 keV neutral atomic hydrogen impact

A complete set of cross sections is reported for the ionization of water molecules by neutral atomic hydrogen impact at velocities of the order of the Bragg peak. The measured relative cross sections are normalized by comparison with proton impact results for the same target conditions and previous absolute data. Event by event coincidence analysis of the product ions and the projectile enables partial cross sections for target ionization and target plus projectile ionization to be determined, as well as total cross sections for electron loss reactions.Comment: To be published in Chemical Physics Letter

INTERACTION OF FAST HYDROGEN IONIC CLUSTERS WITH MATTER

Fast ionic clusters Hn+ interact with matter in a specific way which is observed to deviate strongly from the interaction of atomic ions at the same velocity. We present some results obtained at Lyon about foil and gas interactions of hydrogen clusters (5 ≤ n ≤ 23) at projectile velocities close to the Bohr velocity, i.e. dynamics of the cluster fragmentation, charge state of atomic fragments and absolute dissociation cross sections in gas. We also discuss future experiments specially at higher velocities