Sonia Erattupuzha

Two-pulse control over double ionization pathways in CO2.

We visualize and control molecular dynamics taking place on intermediately populated states during different sequential double ionization pathways of CO2 using a sequence of two delayed laser pulses which exhibit different peak intensities. Measured yields of CO2 (2+) and of fragment pairs CO(+)/O(+) as a function of delay between the two pulses are weakly modulated by various vibronic dynamics taking place in CO2 (+). By Fourier analysis of the modulations we identify the dynamics and show that they can be assigned to merely two double ionization pathways. We demonstrate that by reversing the sequence of the two pulses it becomes possible to control the pathway which is taken across CO2 (+) towards the final state in CO2 (2+). A comparison between the yields of CO2 (2+) and CO(+)/O(+) reveals that the modulating vibronic dynamics oscillate out-of-phase with each other, thus opening up opportunities for strong-field fragmentation control on extended time scales.

Coincidence spectroscopy of high-lying Rydberg states produced in strong laser fields

We demonstrate the detection of high-lying Rydberg states produced in strong laser fields with coincidence spectroscopy. Electron emission after the interaction of strong laser pulses with atoms and molecules is measured together with the parent ions in coincidence measurements. These electrons originate from high-lying Rydberg states with quantum numbers from

Fragmentation of long-lived hydrocarbons after strong field ionization

n\ensuremath{\sim}20

Direct observation of laser-induced O 2 + production from CO 2

up to

Enhanced ionization of acetylene in intense laser pulses is due to energy upshift and field coupling of multiple orbitals

n\ensuremath{\lesssim}120

Molecular oxygen observed by direct photoproduction from carbon dioxide

formed by frustrated field ionization. Ionization rates are retrieved from the measured ionization signal of these Rydberg states. Simulations show that both tunneling ionization by a weak dc field and photoionization by blackbody radiation contribute to delayed electron emission on the nano- to microsecond scale. Furthermore, the dependence of the Rydberg-state production on the ellipticity of the driving laser field indicates that such high-lying Rydberg states are populated through electron recapture. The present experiment provides detailed quantitative information on Rydberg production in strong-field interaction.

Laser-Induced Oxygen Formation from Carbon Dioxide

We experimentally and theoretically investigated the deprotonation process on nanosecond to microsecond timescale in ethylene and acetylene molecules, following their double ionization by a strong femtosecond laser field. In our experiments we utilized coincidence detection with the reaction microscope technique, and found that both the lifetime of the long-lived ethylene dication leading to the delayed deprotonation and the relative channel strength of the delayed deprotonation compared to the prompt one have no evident dependence on the laser pulse duration and the laser peak intensity. Quantum chemical simulations suggest that such delayed fragmentation originates from the tunneling of near-dissociation-threshold vibrational states through a dissociation barrier on a dication electronic state along C--H stretching. Such vibrational states can be populated through strong field double ionization induced vibrational excitation on an electronically excited state in the case of ethylene, and through intersystem crossing from electronically excited states to the electronic ground state in the case of acetylene.

Laser pulse duration can control the breakage of multiple chemical bonds

On the Earth, oxygen molecules are generated mostly via the photosynthesis by green plants and algae from carbon dioxide and water: nCO<inf>2</inf> + nH<inf>2</inf>O ^light→ (CH<inf>2</inf>O)n + nO<inf>2</inf> [1]. Although, theoretical studies showed the possibility of O<inf>2</inf> production via CO<inf>2</inf> fragmentation [2] and experimental investigations achieved the detection of C⁺ (referring the creation of O<inf>2</inf> on the other side) [3], the direct observation of O2 formation did not yet happen to our knowledge. In this submission, we report the direct experimental observation of molecular oxygen formation from carbon dioxide molecule after being doubly ionized by a strong laser pulse.

High-Lying Rydberg States from Strong Field Interaction

Laser-ionization of molecules is one of the most important processes in the strong-field and attosecond sciences. One of the key mechanisms governing molecular ionization is enhanced ionization, where for diatomic molecules the ionization probability becomes strongly enhanced at a critical internuclear distance [1, 2]. Experiments on polytatomic molecules have revealed remarkably high charge states and indicated the existence of a different ionization-enhancement mechanism [3-5]. However, until now this mechanism has not been fully understood and has been a subject of intense debate.

Two-Pulse Control over Double Ionization Pathways in CO2

Oxygen (O2 ) is one of the most important elements required to sustain life. The concentration of O2 on Earth has been accumulated over millions of years and has a direct connection with that of CO2 . Further, CO2 plays an important role in many other planetary atmospheres. Therefore, molecular reactions involving CO2 are critical for studying the atmospheres of such planets. Existing studies on the dissociation of CO2 are exclusively focused on the C–O bond breakage. Here we report first experiments on the direct observation of molecular Oxygen formation from CO2 in strong laser fields with a reaction microscope. Our accompanying simulations suggest that CO2 molecules may undergo bending motion during and after strong-field ionization which supports the molecular Oxygen formation process. The observation of the molecular Oxygen formation from CO2 may trigger further experimental and theoretical studies on such processes with laser pulses, and provide hints in studies of the O2 and O + 2 abundance in CO2 -dominated planetary atmospheres.