Reaction microscope studies of small molecules in strong laser fields

Abstract

The dynamics of molecules and molecular reactions that generate chemistry such as bond breaking, bond formation or bond rearrangement occur on the femtosecond (10ð€€€15 s) time scale. Real-time observations and investigations of these reactions are fundamental to understanding these dynamics. Ultra-fast laser pulses with intensities around 1014 W=cm2, impact on the electronic and nuclear motion on femtosecond timescale. In order to understand the region of transition states between the initial and nal state of a reaction, that determines the fate of the products, detailed experimental investigations are necessary. This work focuses on three separate investigations, one addressing the strong eld control of the electronic dynamics in the hydrogen molecule and two addressing the strong eld ionization dynamics in small but complex hydrocarbon molecule acetylene (C2H2). The pump-probe approach is applied to observe the real-time femtochemistry. The rst part of this thesis deals with the strong eld dissociation of H+ 2 . The goal is to control the dissociating dynamics by utilizing the control capability of the carrierenvelope phase (CEP) in a pump-probe approach. The work shows the response of the bound electron during the dissociation process. The timing of the electron localization and time-dependent distribution of the inter-nuclear separation is retrieved. Second and third part of this thesis deals with the investigations of the fragmentation dynamics in acetylene in the strong laser eld. Time-resolved vibrational dynamics and enhanced ionization (EI) are studied by using the pump-probe approach with reaction microscope in the second part. A wave-packet is launched onto the acetylene cation by the pump pulse and vibrational dynamics are traced by the probe pulse in di-cation fragmentation of the acetylene. Whereas laser parameters to control particular fragmentation and bond breaking are investigated in the third section of the thesis. This is illustrated by taking the experimental measurements at di erent laser intensities and ellipticities and parameters that govern the ultra-fast proton migration in acetylene dication are investigated. It is found that C-C bond breaking after proton migration in acetylene dication is favored in circularly polarized laser elds over C-C bond breaking without proton migration.