Fragmentation dynamics of tetrachloromethane molecule induced by highly charged Ar7+-ion impact.

The ion impact multiple ionization and subsequent dissociation of CCl4 is studied using a beam of Ar7+ ion having the energy of about 1 MeV in a linear time- of-flight mass spectrometer, coupled with a position-sensitive detector. The complete, as well as incomplete Coulomb explosion pathways, for CCl4 2+ and CCl4 3+ ions are identified and studied. The kinetic energy release distributions of channels, kinetic energies, and momentum distributions of fragmented ions, as well as neutrals, are also calculated. Possible modes of fragmentation pathways, i.e., concerted and/or sequential, for all the identified channels are studied using Newton diagrams, Dalitz plots, and kinetic energy distributions. The dynamical information and fragmentation pathways were analyzed with the Dalitz plot and Newton diagram for the three-body dissociation channel. The nature of the fragmentation process is further investigated with simulated Dalitz plots and Newton diagrams using the simple classical mechanical model.

Simultaneous observations of electromagnetically induced transparency (EIT) and absorption (EIA) in a multi-level V-type system of 87Rb and theoretical simulation of the observed spectra using a multi-mode approach.

We report here simultaneous experimental observation of Electromagnetically Induced Transparency (EIT) and Electromagnetically Induced Absorption (EIA) in a multi-level V-type system in D2 transition of Rb87, i.e., F=2→F' with a strong pump and a weak probe beam. We studied the probe spectrum by locking the probe beam to the transition F=2→F'=2 while the pump is scanned from F=2→F'. EIA is observed for the open transition (F=2→F'=2) whereas EIT is observed in the closed transition (F=2→F'=3). Sub natural line-width is observed for the EIA. To simulate the observed spectra theoretically, Liouville equation for the three-level V-type system is solved analytically with a multi-mode approach for the density matrix elements. We assumed both the pump and the probe beams can couple the excited states. A multi-mode approach for the coherence terms facilitates the study of all the frequency contributions due to the pump and the probe fields. Since the terms contain higher harmonics of the pump and the probe frequencies, we expressed them in Fourier transformed forms. To simulate the probe spectrum, we have solved inhomogeneous difference equations for the coherence terms using the Green's function technique and continued fraction theory. The experimental line-widths of the EIT and the EIA are compared with our theoretical model. Our system can be useful in optical switching applications as it can be precisely tuned to render the medium opaque and transparent simultaneously.

Imaging molecular structure through femtosecond photoelectron diffraction on aligned and oriented gas-phase molecules.

This paper gives an account of our progress towards performing femtosecond time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe setup combining optical lasers and an X-ray free-electron laser. We present results of two experiments aimed at measuring photoelectron angular distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C(8)H(5)F) and dissociating, laser-aligned 1,4-dibromobenzene (C(6)H(4)Br(2)) molecules and discuss them in the larger context of photoelectron diffraction on gas-phase molecules. We also show how the strong nanosecond laser pulse used for adiabatically laser-aligning the molecules influences the measured electron and ion spectra and angular distributions, and discuss how this may affect the outcome of future time-resolved photoelectron diffraction experiments.

Excited state intramolecular proton transfer in 3-hydroxy flavone and 5-hydroxy flavone: a DFT based comparative study.

Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of 3-hydroxy-flavone (3HF) and 5-hydroxy-flavone (5HF) were studied using DFT/B3LYP (6-31G (d,p)) and TD-DFT/B3LYP (6-31G (d,p)) level of theory respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer for both the compounds. Calculated PE curves of 3HF for the ground and excited singlet states proton transfer process explain its four state laser diagram. Excited states PE calculations support the ESIPT process to both 5HF and 3HF. The difference in ESIPT emission process of 3HF and 5HF have been explained in terms of HOMO and LUMO electron distribution of the enol and keto tautomer of these two compounds.

DFT based computational study on the excited state intramolecular proton transfer processes in o-hydroxybenzaldehyde.

Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of o-hydroxybenzaldehyde (OHBA) were studied using DFT-B3LYP/6-31G(d) and TD-DFT-B3LYP/6-31G(d) level of theory, respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer in this compound. Excited states PE calculations support the ESIPT process in OHBA. The contour PE diagram and the variation of oscillator strength along the proton transfer co-ordinate support the dual emission in OHBA. Our calculations also support the experimental observations of Nagaoka et al. [S. Nagaoka, U. Nagashima, N. Ohta, M. Fujita, T. Takemura, J. Phys. Chem. 92 (1988) 166], i.e. normal emission of the title compound comes from S(2) state and the red-shifted proton transfer band appears from the S(1) state. ESIPT process has also been explained in terms of HOMO and LUMO electron density of the enol and keto tautomer of OHBA and from the potential energy surfaces.

Butterfly structure: signature of vibrational flopping in dissociative acetylene.

We report experimental evidence for molecular deformation due to a vibrationally active transition state of multiply charged acetylene molecules under the impact of low energy Ar8+ projectiles. "Butterflylike" structures are observed in the experimental coincidence spectra between hydrogen and carbon ionic fragments. Such structures can be generated by numerical simulations and are found to originate from the bending motion of the dissociating molecule. Angular distributions for dissociation products from triply charged C2H2 ion are reported.

Formation of H3+ due to intramolecular bond rearrangement in doubly charged methanol.

We report the formation of H3+ by proton coagulation in methanol under the impact of low energy Ar(8+) projectiles. Our time-of-flight coincidence measurements with CH3OD establish that the H3+ formation arises from intramolecular bond rearrangement of the methyl group. We have performed ab initio quantum chemical calculations that show the preferred pathway for C-H3 bond cleavage. Fragmentation of organic molecules like methanol under impact of highly charged ions is suggested as an alternative mechanism of H3+ formation in outer space.