Laser induced alignment of state-selected CH3I

Orientation of Chiral Molecules by External Electric Fields: Focus on Photodissociation Dynamics

Molecular orientation is a fundamental requirement to study and control photoinitiated reactions. Experimental setups that make use of hexapolar electric filters combined with slice-ion imaging detectors were employed in these last years to investigate the photodissociation dynamics of chiral molecules. The final goal is the on-the-fly discrimination of oriented enantiomers, revealed by the different angular distributions in photofragment ion-imaging, as predicted from vector correlation studies. Here, we review experiments of photodissociation of oriented chiral molecules, with the aim of presenting limits emerging from these investigations and perspectives toward the achievement of the ultimate objective.

Ultrafast proton migration and Coulomb explosion of methyl chloride in intense laser fields

We investigated the ultrafast proton migration and the Coulomb explosion (CE) dynamics of methyl chloride (CH₃Cl) in intense femtosecond laser fields at the wavelengths of 800 nm (5.5 × 10¹⁴ W/cm²) and 400 nm (4 × 10¹⁴ W/cm²), respectively. Various fragment channels from molecular dication and trication were observed by coincidence momentum imaging through the measurement of their kinetic energy releases (KERs). The proton migration from different charged parent ions was analyzed from the obtained KER distributions. For the direct CE channel of CH₃⁺ + Cl⁺ and CH₃⁺ + Cl²⁺, the contribution of multiply excited electronic states and multicharged states is identified. In addition, the measurements of relative yields of the fragmentation channel at different laser wavelengths provide a selective control of proton migration for CH₃Cl molecules in intense laser fields.

Rotational Dynamics of Quantum State-Selected Symmetric-Top Molecules in Nonresonant Femtosecond Laser Fields

Rotational dynamics of quantum state selected and unselected CH₃I molecules in intense femtosecond laser fields has been studied. The orientation and alignment evolutions are derived from a pump-probe measurement and in good agreement with the numerical results from the time-dependent Schrödinger equation (TDSE) calculation. The different rotational transitions through nonresonant Raman process have been assigned from the Fourier analysis of the orientation and alignment revivals. These revivals are derived from a pump-probe measurement and in good agreement with the numerical results from the TDSE calculation. For the molecules in rotational state |1, ±1, ∓1⟩, the transitions can be assigned to ΔJ = ±1, ±2, while for thermally populated molecules, the transitions are ΔJ = ±2. Our results illustrate that the orientation and alignment revivals of the rotational quantum-state-selected molecules give a deep insight into the rotational excitation pathways for the transition of different rotational states of molecules in ultrafast laser fields.