O2 Production from CO2 with Ultrashort Lasers

O2 production is one of the most important processes on the earth for the biosphere. Oxygen molecules are mainly generated via the photosynthesis by green plants and algae from carbon dioxide and water. CO2 is not only important to the atmosphere on the Earth; it is also the dominant compound of the atmosphere on many other planets, such as Mars and Venus. One of the most important tasks for the mission to establish a human settlement on Mars is to produce O2. Because more than 95% of the atmosphere on the Mars is CO2, it will be ideal if O2 can be produced direct from CO2. Dissociation of a CO2 molecule via absorption of photons or collision with high energy electrons exclusively leads to a carbon monoxide (CO) and an oxygen atom (O). However, theoretical studies suggested the possibility of producing O2 through the dissociation of a CO2 molecule. A recent experiment showed the evidence of O2 formation from CO2 molecules after excitation by ultraviolet radiation through the detection of C+. So far, there is no direct observation of O2 formation from CO2. In the past decade, intense ultrashort laser pulses have been already successfully applied to trigger and control molecular reactions, such as dissociation and isomerization. When a molecule is exposed in a strong laser pulse, electrons can be excited or removed which leads the molecule into an excited or a certain charge state. As a result, the geometry of the excited or ionized molecule may undergo severe reconfiguration and the molecule may break into several pieces or new chemical bonds can be formed afterwards. Because of the importance of CO2 to many research disciplines, strong field induced reactions of CO2 have been already experimentally studied with ultrashort lasers by several research groups. However such studies are mainly focused on the topic of ionization and dissociation into CO+ and O+. In this proposal, we plan to systematically explore of the O2 formation from CO2 induced by ultrashort laser pulses with coincidence detection by using a reaction microscope. Quantum chemical calculations will be performed to understand the experimental observations and interpret the mechanism of the O 2 formation from CO2. Further, we propose research on adaptive control of the O2 formation process by shaping the temporal structure of femtosecond laser pulses and on optimizing the efficiency of the O2 formation from CO2 for potential applications.

In this project, we carried out experimental studies of electron and nuclear dynamics in laser-induced molecular reactions, which include the dissociation (bond breakage) and isomerization (O2 bond formation) processes. Using a reaction microscope, we recorded charged particles from the laser-induced molecular reactions. From the measured signals with different laser parameters, we revealed the involved electron dynamics during the laser-induced molecular ionization and excitation, and further resulting nuclear dynamics leading to the bond breakage and formation reactions. In the frame of the project, we achieved the following results: With the channel-resolved measurements, we obtained the branching ratios of different molecular reactions of CO2 in a laser field. The same dependence of the branching ratios on the laser intensity indicates that the bond breakage and bond formation process after double ionization of CO2 has the same origin. We experimentally investigated the laser-induced dissociative recombination processes of CO2 with coincidence detection of all involved particles. The measured kinetic energy released and electron momentum distributions allow for the understanding of both nuclear and electron dynamics during the laser-induced dissociative recombination of CO2. Our measurements clearly show that the laser-induced dissociative recombination of CO2 originates from the recombination of one electron to one of the two ionic fragments during laser-induced dissociative double ionization. We demonstrated a time-domain method to quantitatively retrieve the angular dependence of electron rescattering from nondissociative and dissociative nonsequential double ionization of molecules. We demonstrate this approach by performing measurements and retrievals using the CO2 molecule as an example. In the retrieval procedure, we used the channel resolved ionization signals in combination with the in situ measured angular distribution of the field-free molecular alignment from the coincidence measurements with a reaction microscope, such that the effect of molecular alignment quality can be excluded in the retrieved result. We studied electron trapping processes during strong-field double ionization of argon atoms using three-body coincidence measurements. We observed a strong enhancement of the trapping probability after strong-field double ionization in comparison with single ionization. The measured intensity dependence of this enhancement indicates that in the sequential double ionization regime the trapping process is dominated by the second detached electron. In the nonsequential double ionization regime, we find that the trapping probability is strongly suppressed as compared to that in the sequential double ionization regime. We attribute this to a strong correlation between the two electrons.