Mass spectrometric and charge density studies of organometallic clusters photoionized by gigawatt laser pulses

Abstract

Clusters on exposure to nanosecond laser pulses of gigawatt intensity exhibit a variety of photo-chemical processes such as fragmentation, intracluster reaction, ionization, Coulomb explosion, etc. Present article summarizes the experimental results obtained in our laboratory utilizing time-of-flight mass spectrometer which deal with one such aspect of cluster photochemistry related to generation of multiply charged atomic ions upon excessive ionization of cluster constituents (Coulomb explosion) at low intensity laser field (∼10 W/cm ). To understand the mechanism of laser-cluster interaction, laser as well as cluster parameters were varied. Mass spectrometric studies were carried out at different laser wavelength as well as varying the nature of cluster constituents, backup pressure, nozzle diameter, etc. In addition, charge density measurements were also preformed to get information about the total number of ions generated upon laser-cluster interaction as a function of laser wavelength. In case of pure molecular clusters, the charge state of atomic ions as well as charge density was observed to enhance with increasing laser wavelength, signifying efficient coupling of the cluster medium with nanosecond laser pulse at longer wavelength. While in case of clusters doped with species having comparatively lower ionization energy, the efficiency of laser-cluster interaction was less, in contrast to studies carried out using femtosecond lasers. Results obtained in the present work have been rationalized on the basis of proposed three-stage cluster ionization mechanism, that is, multiphoton ionization ignited-inverse Bremsstrahlung heating and electron ionization. © 2015 Wiley Periodicals, Inc. Mass Spec Rev. 36:188-212, 2017.

Production of Multiply Charged Argon Ions in Moderate Nanosecond Laser Fields: An Open Question or a Forgone Conclusion?

“…The role of resonance is to provide a facile pathway of ionization for Ar, and given the field strength and the related line-broadening, many levels can come into resonance and achieve the resonant enhancement of coherent multiphoton absorption. In fact, we believe that this is exactly the case for neat molecular clusters with many vibronic levels available for resonant enhancement. ,− …”

“…Among the three major points raised by VM, we are in full agreement with the authors on the limited role of the chromophore and the beneficial effect of resonance for the formation of Ar + . In the introduction of our Letter, references to a variety of compounds investigated by three other groups are listed, − and the lack of a common structural motif among the compounds implies that a chromophore is not the prerequisite to observe MCAIs. Our path of ionization for Ar + is specific only to our own experiment and is not intended to be general: the path with the resonances is the enhanced path, offering a higher probability of excitation than otherwise.…”

Multiple ionization and Coulomb explosion of molecules, molecular complexes, clusters and solid surfaces

“…However, it should be mentioned that Coulomb explosion of clusters followed by the ejection of ions with large charge number and high energy occurs even by using nanosecond laser pulses [22,23]. In the cases of the Coulomb explosion processes initiated by using nanosecond and/or picosecond laser pulses, clusters can relax to their most stable structures and, thus, information about the initial configuration is lost.…”

“…When the charge numbers of MMCs are large enough, the energies released in Coulomb explosion are easily several tens of eV, which is significantly more than typical chemical bonding energies. Coulomb explosion processes have been discussed for molecules [20] and clusters [21][22][23] in the gas phase. In contrast, Coulomb explosions of solids such as metals, dielectrics, semiconductors, polymers, and molecular crystals have been less emphasis even in recent reviews of the subject [24][25][26][27].…”

Multiply charged energetic metal ion emissions from dinuclear metal complex exposed to intense femtosecond laser fields

“…At the same time, the productions of multiply charged metals as well as their large kinetic energy release in clusters have also been reported by using nanosecond laser pulses. [29,30] Several ionization and relaxation mechanisms in clusters have been proposed, and controversy as to arguments regarding the energy gain mechanism is ongoing. [31][32][33] Kinetic energy of ions formed in clusters is not simply explained by the interaction between ions but by the collective effect of many atoms, atomic ions, and electrons.…”