G. S. Lodha

Bio: G. S. Lodha is an academic researcher from Raja Ramanna Centre for Advanced Technology. The author has contributed to research in topics: Photon energy. The author has an hindex of 1, co-authored 3 publications receiving 16 citations.

Triply charged carbon dioxide molecular ion: Formation and fragmentation

Abstract: In an experiment involving detection of a photoelectron and up to three photoions from CO{sub 2} in coincidence, we observe the triple ion coincidence C{sup +}:O{sup +}:O{sup +}. Moreover, we observe double coincidences between doubly charged cations and singly charged cation pairs C{sup 2+}:O{sup +}, O{sup 2+}:C{sup +}, O{sup 2+}:O{sup +}. These ion triplets and pairs arise from fragmentation of the triply charged molecular ion CO{sub 2}{sup 3+}. Other ion pairs--viz., C{sup +}:O{sup +}, O{sup +}:O{sup +}, O{sup +}:CO{sup +}--arising from the doubly charged molecular ion CO{sub 2}{sup 2+}, are also observed. From an analysis of the coincidence pattern we postulate four decay modes of the CO{sub 2}{sup 3+} ion. Kinetic energy release in the channel leading to C{sup +}:O{sup +}:O{sup +} is measured, and its distribution is postulated to have four contributing precursor states.

Dissociative photo-multiple-ionisation of CO and CO2

Abstract: In a photoelectron–photoion coincidence experiment on CO and CO2, we have observed the formation and fragmentation of singly to triply charged CO2 and singly to quadruply charged CO at various energies. Doubly charged cations of both molecules are found to have unstable as well as stable states. Cations with higher charge are found to dissociate promptly. The energy dependence of the relative partial cross-sections in the energy range 125–310 eV are presented.

Fragmentation dynamics of CO(2)(3+) investigated by multiple electron capture in collisions with slow highly charged ions.

Abstract: Fragmentation of highly charged molecular ions or clusters consisting of more than two atoms can proceed in a one step synchronous manner where all bonds break simultaneously or sequentially by emitting one ion after the other. We separated these decay channels for the fragmentation of CO(2)(3+) ions by measuring the momenta of the ionic fragments. We show that the total energy deposited in the molecular ion is a control parameter which switches between three distinct fragmentation pathways: the sequential fragmentation in which the emission of an O(+) ion leaves a rotating CO(2+) ion behind that fragments after a time delay, the Coulomb explosion and an in-between fragmentation--the asynchronous dissociation. These mechanisms are directly distinguishable in Dalitz plots and Newton diagrams of the fragment momenta. The CO(2)(3+) ions are produced by multiple electron capture in collisions with 3.2 keV/u Ar(8+) ions.

Communication: Determining the structure of the N2Ar van der Waals complex with laser-based channel-selected Coulomb explosion

Abstract: We experimentally reconstructed the structure of the N2Ar van der Waals complex with the technique of laser-based channel-selected Coulomb explosion imaging. The internuclear distance between the N2 center of mass and the Ar atom, i.e., the length of the van der Waals bond, was determined to be 3.88 A from the two-body explosion channels. The angle between the van der Waals bond and the N2 principal axis was determined to be 90° from the three-body explosion channels. The reconstructed structure was contrasted with our high level ab initio calculations. The agreement demonstrated the potential application of laser-based Coulomb explosion in imaging transient molecular structure, particularly for floppy van der Waals complexes, whose structures remain difficult to be determined by conventional spectroscopic methods.

Dissociation of carbonyl sulfide by 150 keV Ar+ ion impact

Abstract: We report on the formation and dissociation of the multiply charged carbonyl sulfide (OCS) molecular ions, OCSq + (where q = 1?4), formed in the collision of neutral OCS molecules with 150 keV Ar+ projectiles, detected using coincidence techniques. From the coincidence map of the fragments we have separated complete two- and three-body dissociation channels resulting in various ionic fragments. Comparing the slope of the coincidence islands with theoretical values, determined from the charge and momentum distribution of the correlated particles, we postulate different decay modes behind each of the fragmentation channels. We also discuss momentum imaging and the kinetic energy release of each of the dissociation channels of OCSq +, which give further information about the momentum balance and the geometry of the precursors in OCS fragmentation.

Three-body fragmentation of CO2 driven by intense laser pulses.

Abstract: Dissociative ionization dynamics were studied experimentally for CO2 driven by intense laser pulses. Three-dimensional momentum vectors of correlated atomic ions were obtained for each three-body fragmentation event using triple ion coincidence measurement. Newton diagram demonstrated that three-body fragmentation of CO2 (n+) (n = 3-6) can occur through Coulomb explosion process and sequential fragmentation process depending on the fragmentation channels. The experimental data from these two processes were disentangled by using correlation diagram of correlated ions. Based on the accurate Coulomb explosion data, we reconstructed the bond angle distributions of CO2 (n+) at the moment of fragmentation, which are close to that of neutral CO2 before laser irradiation.

Formation, structure, and dissociation dynamics of CO 2 q+ (q≤3) ions due to impact of 12-keV electrons

Abstract: The electron-impact multiple ionization and subsequent dissociation of CO${}_{2}$ is studied for 12-keV electron energy using a linear time-of-flight mass spectrometer coupled with a multihit, position-sensitive detector. The complete as well as incomplete Coulomb explosion pathways for CO${}_{2}$${}^{2+}$ and CO${}_{2}$${}^{3+}$ ions are examined and identified. The kinetic energy release distributions for these precursor ions are obtained. The experimental kinetic energy release values for the complete Coulomb fragmentation channels are found to be overestimated by those calculated from the Coulomb explosion model. From the angular correlation studies, it is inferred that bent geometrical states are involved for most of the fragmentation channels of CO${}_{2}$${}^{2+}$ and CO${}_{2}$${}^{3+}$ ions. The concerted and/or sequential nature of all the dissociation pathways is also assigned. This study provides the first results on energetics associated with the charge separation in dissociative ionization of CO${}_{2}$ under the impact of electrons at a subrelativistic energy.