Jyoti Rajput

• PhD
• Professor at University of Delhi

The two-body dissociation of the dications formed after double ionization of the smallest conjugated diene, the 1,3-butadiene, C4H6, is studied using the coincidence time-of-flight technique and quantum chemistry calculations. The dication was formed by ion-impact ionization using energetic Xe3+ projectiles. Our results show that butadiene dication...

The three body fragmentation of methane dication has been studied using the technique of cold target recoil ion momentum spectroscopy. The process is initiated by impact of energetic Ar 9+ ions on neutral methane and the data is subsequently collected in coincidence with Ar 8+ projectile. By analysing the dissociation channels leading to (H + H + +...

The three body breakup of [C 2 H 2 ] ³⁺ formed in collision with Xe ⁹⁺ moving at 0.5 atomic units of velocity is studied using recoil ion momentum spectroscopy. Three body breakup channels leading to (H ⁺ , C ⁺ , CH ⁺ ) and (H ⁺ , H ⁺ , C 2 ⁺ ) fragments are observed in the experiment and their kinetic energy release is measured. The breakup into (...

We report on the direct experimental evidence of hydrogen migration in triply charged acetylene. The roaming hydrogen atom in a triply charged molecular ion is counter intuitive. The three body breakup channel [Formula: see text] is studied using the technique of recoil ion momentum spectroscopy. The triply charged ion was generated in collisions o...

The ion-induced fragmentation of CH4²⁺ into H⁺$^+$ and CH3⁺ is studied using cold target recoil ion momentum spectroscopy in coincidence with the charge state of the post-collision projectile. Using constant velocity Ar⁹⁺ and N³⁺, results from four different data sets are presented, with a selection on the final charge state of the projectile (Ar⁸⁺...

Singly and multiply charged molecular ions are found in diverse environments and hold relevance for a wide range of research areas like combustion chemistry, accelerator physics, atmospheric sciences, plasma physics, astrophysics etc. Molecular dications are of special significance as they can be generated and studied comparatively easily in labora...

Objectives To explore the two-body dissociation channels populated in collision of slow highly charged ion with neutral SO 2 molecules. To study an angular distribution of recoil ion fragments with respect to direction of incoming ion beam for a non-linear triatomic molecule. Conclusions (1) The angular distributions of fragment ions with respect t...

Objectives To explore the two-body dissociation channels populated in collision of slow highly charged ion (129 Xe 9+) with neutral OCS molecules. To determine the relative branching ratios of all the populated two body channels. To study an angular distribution of recoil ion fragments with respect to direction of incoming ion beam. Future outlook...

Objectives To explore the three-body dissociation of the triatomic molecule SO 2 q+ formed in collision of the neutral parent with a slow highly charged ion. To measure relative branching ratios for the observed dissociation channels. To check for the active decay mechanisms (sequential vs concerted) involved in the observed three body breakup chan...

We investigate intense, ultrafast laser-induced isomerization and two-body fragmentation of acetylene monocations and dications using coincidence three-dimensional momentum imaging. Whereas the vast majority of previous work on strong-field isomerization and fragmentation of acetylene has necessarily involved ionization, by focusing solely on disso...

Synopsis The two-body dissociation of multiply charged SO 2 molecules is studied using a recoil ion momentum spectrometer. These molecular ions were generated in collision of the neutral parent with an energetic highly charged ion. From the measured momenta of the recoil ions, angular distributions are generated with respect to the incoming beam di...

Synopsis Multiply charged ion impact induced three body fragmentation pathways of SO 2 q + (q=3, 4) molecular ions have been studied using the technique of recoil ion momentum spectroscopy. An attempt has been made to distinguish the three-body breakup based on mechanism of dissociation, whether sequential or concerted.

A comparative study of bond rearrangement is reported for the double ionization of three triatomic molecules: carbon dioxide, carbonyl sulfide, and water (D2O). Specifically, we study the formation of the molecular cation AC+ from the edge atoms of a triatomic molecular dication ABC2+ following double ionization by intense, short (23 fs, 790 nm) la...

A key question concerning the three-body fragmentation of polyatomic molecules is the distinction of sequential and concerted mechanisms, i.e., the stepwise or simultaneous cleavage of bonds. Using laser-driven fragmentation of OCS into O++C++S+ and employing coincidence momentum imaging, we demonstrate a novel method that enables the clear separat...

Events from the sequential and concerted modes of the fragmentation of OCS³⁺ that result in coincident detection of fragments C⁺, O⁺, and S⁺ have been separated using a newly proposed representation. An ion beam of 1.8 MeV Xe⁹⁺ is used to make the triply charged molecular ion, with the fragments being detected by a recoil ion momentum spectrometer....

We investigate dissociation in flight of metastable molecular dications formed by ultrashort, intense laser pulses using the cold target recoil ion momentum spectroscopy technique. A method for retrieving the lifetime(s) of the transient metastable state(s) as well as the complete three-dimensional momenta of the dissociating fragments is presented...

Three body fragmentation pathways of OCS³⁺ molecular ion leading to detection of C ⁺ + O ⁺ + S ⁺ in coincidence have been studied using the technique of recoil ion momentum spectroscopy. This fragmentation can occur either via a one step concerted process or a two step sequential process. In the first step of the sequential pathway either CO²⁺ or C...

Several two-body dissociation channels of multiply ionized OCS molecules generated by Xe⁹⁺ impact are studied for the angular distributions of fragment ions with respect to the incident projectile direction. We have used the technique of recoil ion momentum spectroscopy (RIMS) for measuring momenta of the fragment ions in coincidence.

The angular distribution of fragment emission with respect to the incoming beam direction is measured. In case of two body breakup of di-cationic molecular ions, such as D2O²⁺ and , a strong anisotropy is observed when one of the fragments is an H⁺ or D⁺. These molecular ions were produced by impact of slow highly charged ions on neutral species. T...

We investigate bond-rearrangement driven by photo-double-ionization (PDI) near and above the double-ionization threshold in a sequence of carbon-carbon double-bonded hydrocarbon molecules: ethylene, fluoroethylene, and 1,1-difluoroethylene. We employ the kinematically complete cold target recoil ion momentum spectroscopy method to resolve all photo...

The angular distribution of the correlated molecular fragments with respect to the incoming beam direction for several of dissociation channels of multiply charged N2 molecule on collision with Xe9+ was studied.

Collective excitation in polycyclic aromatic hydrocarbon molecule is studied in collision experiments with intermediate velocity (50-180 keV) proton and FUV (15-40 eV) photon energy. In proton impact experiments a clear comparison between pure ionization and capture ionization (or pure capture) process is done on the basis of ionization, evaporatio...

We report the angular distribution of the fragment ions formed in the collision of Xe⁹⁺ ions with isolated water molecules. A significant anisotropy, and strong alignment effects have been seen. It is observed that there is a strong forward - backward asymmetry in the emission of protons and oxygen ions in the three body dissociation of multiply ch...

Electronic energy loss distribution estimation is done under local density distribution using Monte Carlo simulations. These results are used to compare the experimental results of proton-polycyclic aromatic hydrocarbons (PAHs) and proton-nucleobase interactions at intermediate velocity collisions.

We report a novel technique to measure the plasma potential. In this technique, we extract an ion beam into the chamber with few keV of energy and then decelerate it using series of electrodes till the deceleration potential nullifies the extraction potential and measure the retaining energy of the beam using retarding plate analyzer (RPA) to deter...

The technique of recoil ion momentum spectroscopy is employed to determine the complete momentum vectors for three fragment dissociation channels, [D2O]((q+2)) → (D(+) + D(+) + O(q+)) with q = 1, 2, or 3 formed in collisions of isolated water molecules with 450 keV Xe(9 +) ions. The kinetic energy released in each of these dissociation channels is...

A recoil ion momentum spectrometer has been fabricated for studying angular anisotropies in ion-induced molecular dissociation. The spectrometer is characterized for its time and momentum resolution by studying test cases of ion-atom and ion-molecule collisions. The typical time resolution is measured to be 2.9 × 10−3(Δt/t) and typical momentum res...

Members of the green fluorescent protein (GFP) family may undergo irreversible phototransformation upon irradiation with UV light. This provides clear evidence for the importance of the higher-energy photophysics of the chromophore, which remains essentially unexplored. By using time-resolved action and photoelectron spectroscopy together with high...

Members of the green fluorescent protein (GFP) family may undergo irreversible phototransformation upon irradiation with UV light. This provides clear evidence for the importance of the higher-energy photophysics of the chromophore, which remains essentially unexplored. By using time-resolved action and photoelectron spectroscopy together with high...

We investigate the interaction of a high velocity proton projectile (velocity between 1.41 and 2.68 au) with a gaseous naphthalene target. Fragmentation as well as multiple ionization yields are measured from the resulting mass spectra. The total fragmentation yields decrease with an increase in projectile velocity, which is in accordance with decr...

We investigate the fragmentation and ionization of naphthalene by protons at intermediate velocities (between 1.41 and 2.68 a.u.). Relative cross sections for electron capture (EC), electron emission (EE), and capture ionization are measured. The EC cross sections decrease rapidly over the energy range under consideration (50–150 keV) and are lower...

The fragmentation, initiated by photoexcitation as well as collisionally-induced excitation, of several retinal chromophores was studied in the gas phase. The chromophore in the protonated Schiff-base form (RPSB), essential for mammalian vision, shows a remarkably selective photoresponse. The selectivity of the gas-phase chromophore is triggered by...

We report on the formation of fast, energetic Rydberg Hydrogen atoms in the ion impact dissociation of water molecules. The kinetic energies of the neutral atoms have been determined by position sensitive time of flight measurements. The energies of the fast neutral atoms are similar to those observed in extra-solar planets. These can also act as a...

Gas phase photoabsorption measurements on model chromophores can be useful in shedding light on the issue of spectral tuning within photoactive proteins. In nature, protein pockets holding chromophores often form one or more H-bonds with the chromophore, which almost always participates in the photocycle of the protein. We address the issue of spec...

Dissociation of isolated water molecules has been addressed using the technique of time-of-flight spectrometry employing multi-hit detection in an ion-molecule collision experiment. Ar9+ ions having energy of 450 keV were used as projectiles for inducing dissociation. We have detected neutral fragments (fast, energetic Rydberg hydrogen atoms) origi...

An electrostatic, cylindrical deceleration lens has been designed, fabricated and tested to slow down beams of highly charged ions. Highly charged ions from an electron cyclotron ion source at a few tens of keV per charge state are decelerated to a few eV/q using the electrostatic lens. The lens enables the study of the interaction of highly charge...

Photodissociation lifetimes and fragment channels of gas-phase, protonated YAn (n = 1,2) peptides and their dimers were measured with 266 nm photons. The protonated monomers were found to have a fast dissociation channel with an exponential lifetime of ∼200 ns while the protonated dimers show an additional slow dissociation component with a lifetim...

The fragmentation of isolated water molecules on collision with 450-keV Ar${}^{9+}$ has been studied using time-of-flight mass spectrometry employing multihit detection. The kinetic energy release spectrum for the dissociation of ${[{\text{H}}_{2}\text{O}]}^{2+$\star${}}$ into (${\text{H}}^{$\star${}},{\text{H}}^{+},{\text{O}}^{+}$) fragments has b...

We report the formation of energetic neutral Rydberg hydrogen atoms and transient Rydberg molecular ions, [(H(2)O)(q+)](⋆) in ion-impact dissociation of isolated water molecules. The kinetic energy spectra of the neutral Rydberg H atoms are determined from the complete study of (H(⋆), H(+), O(+)) dissociation channel. This channel of water dissocia...

Aluminum cluster anions were stored in an electrostatic ion storage ring and irradiated by a laser pulse. Neutral as well as charged decay products emitted 20 s after the excitation were identified and recorded using the daughter ion mass spectrometry method. Besides delayed electron detachment, only monomer emission was observed for Al. The branch...

The design and implementation of a purely electrostatic deceleration lens used to obtain beams of highly charged ions at very low energies is presented. The design of the lens is such that it can be used with parallel as well as diverging incoming beams and delivers a well focused low energy beam at the target. In addition, tuning of the final ener...

The sub-microsecond dissociation pathways for the protonated and deprotonated forms of adenosine 5'-monophosphate were probed in the gas phase using a linear time of flight spectrometer. The studies show two dissociation pathways for the AMP ions indicating dominant ergodic pathways in the photodissociation of these species. The photofragmentation...

Sichtbares Licht: Ein kombinierter experimenteller und theoretischer Ansatz führte zu hochaufgelösten Gasphasenabsorptionsspektren derjenigen Chromophorkonformationen, die bei der spektroskopischen Untersuchung von Retinalproteinen von Bedeutung sind (siehe Bild). Viele Retinalpigmente absorbieren nahe den für die Gasphase ermittelten Werten.

Model compounds of the green fluorescent protein (GFP) phenolate chromophore are synthesized and investigated for their intrinsic optical properties by state-of-the-art gas-phase action spectroscopy.

Spectral tuning in the photoactive yellow protein (PYP) is investigated by performing gas-phase absorption measurements on a PYP-model chromophore with two water molecules hydrogen-bonded to it. The photoabsorption maximum shows an unusually large blue shift of 0.71 eV in going from the bare to the hydrogen-bonded chromophore. It is concluded that...

We report on gas-phase experimental and theoretical studies on the neutral form of the green-fluorescent protein (GFP) chromophore using six different models, each carrying a spectator positive charge. Theoretical studies were carried out to quantify the effect of the spectator charge on the absorption maximum of the true neutral. The study also in...

Photoabsorption spectra of deprotonated trans p-coumaric acid and two of its methyl substituted derivatives have been studied in gas phase both experimentally and theoretically. We have focused on the spectroscopic effect of the location of the two possible deprotonation sites on the trans p-coumaric acid which originate to either a phenoxide or a...

The absorption dynamics of two model chromophores of the photoactive yellow protein were studied in gas-phase experiments. Using different time-resolving techniques with an overall sensitivity ranging from seconds down to a few nanoseconds, complex dynamics were revealed for the p -coumaric acid anion, involving both fragmentation and electron deta...

The dissociation dynamics of multiply charged methanol molecules formed in collision with 1.2MeV Ar8+projectiles is studied. Using coincidence mapping techniques, we can separate out the different dissociation pathways between carbon, oxygen and hydrogen ionic fragments as well as two- and three-body breakup events. Reactions involving intramolecul...

We report the results of dissociation dynamics of multiple charged acetylene molecules formed in collision with 1.2 MeV Ar^8+ projectiles. Using the coincidence map, we found the evidence for molecular deformation due to a vibrationally active transition state of multiply charged C2H2 under the impact of low energy projectiles. `Butterfly-like' str...

The lifetime of the SF6 anion was measured at the electrostatic ion storage ring ELISA, where decays in the time span from 100 mus to a few seconds were recorded. We find a nonexponential decay with an approximate t(-1.5) power-law dependence. The observed decay rate is accounted for by a model for thermionic emission that takes into account the in...

We report on the results of dissociation dynamics of multiple charged acetylene molecules formed in collision with 1.2 MeV Ar8+ projectiles. Using the coincidence map, we can separate out the different dissociation pathways between carbon and hydrogen ionic fragments as well as complete two-body breakup events. From the measured slopes of the coinc...

The projectile charge-state dependence of methane fragmentation is studied at a constant projectile (Arq+, 1≤q≤7) velocity of 0.42 a.u. using the technique of time-of-flight mass spectroscopy. The relative cross sections for fragment production are reported as a function of the incident projectile charge state. The fragments appearing as molecular...

We report here the results of dissociation of multiple charged methanol and acetylene molecules in collision with 1.2 MeV Ar8+ projectiles. We observed a wide range of dissociation products from the TOF spectrum starting from undissociated molecular ions, fragments losing an hydrogen atom due to breakage of C–H and/or O–H bonds, to complete rupture...

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 generate...

Ion-induced molecular fragmentation of CO has been studied using time-of-flight mass spectroscopy with position sensitive detectors in multihit coincidence mode. Ar8+ ions having a velocity of 1.1 a.u. were used as projectiles. The features observed in the kinetic energy release (KER) spectra for all the detected fragmentation channels are discusse...

We report here results of TOF multi-hit coincidence experiment [1] that provide evidence for intramolecular reactions involving proton coagulation in methanol [2] after interaction with 1.2 MeV Ar^8+ projectiles produced from the ECR ion source in the LEIBF laboratory of Inter-University Accelerator Centre, India. Quite remarkably, we have observed...

Target excitation following ion-impact has been observed to play a significant role in multi-electron capture studies in ion-atom collision experiments. Probably this is the first report on the role of target excitation in ion-induced fragmentation of nitrogen [1]. The multiple ionization and fragmentation of N2 by ion impact is studied using posit...

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 preferr...

The multiple ionization and fragmentation of Nâ induced by ion impact is studied using time- and position-sensitive detectors in multihit coincidence mode. With Ar{sup 9+} at a projectile velocity of 1 a.u., we observe a total of seven fragmentation channels originating from multiply charged transient molecular ions. The preference of symmetric cha...

Dissociative ionisation of molecules can be brought about by various means. Partial cross-sections for fragments arising from dissociative ionisation are a strong function of energy. The yield of ions can be measured by a mass spectrometer; a TOF MS is suitable for this purpose. However in the dissociative ionization process, many product channels...