Chuncheng Wang

Extraction of electron?ion differential scattering cross sections for C2H4 by laser-induced rescattering photoelectron spectroscopy

We have measured angle-resolved rescattering electron momentum distributions for C2H4 generated by intense infrared laser pulses and extracted large-angle elastic differential cross sections (DCSs) for electrons scattering from C2H4+. The angle-dependent ionization rate describing the initial single-ionization step favours ionization from molecules that have their molecular plane aligned perpendicular to the laser polarization direction. The extracted DCSs are well reproduced by the theoretical calculation. We demonstrate that DCSs for electron–ion scattering of the nonlinear polyatomic molecule can be extracted from the laser-induced rescattering electron spectra.

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.

Multielectron Effects in the Strong Field Sequential Ionization of Aligned CH3I Molecules

Strong field sequential ionization of symmetric-top CH3I molecules is studied experimentally by using a combined method of femtosecond laser-induced impulsive alignment and time-of-flight mass spectrometry. Both alignment- and angular-dependent ion yields have been measured, and the sequential ionization of a multielectron has been discussed. It is found that the maximum ionization occurs when the polarization of probe laser is perpendicular to the internuclear axis of molecules, and the signal of fragment ion peaks at the polarization of the probe laser is parallel to the internuclear axis of molecules. The angular distribution of ions indicated that ionization of π-type orbitals corresponds to generation of charged parent ions and ionization of σ-type orbitals corresponds to generation of fragment ions. The sequential release of multielectrons for Coulomb explosion channels is studied by analysis of the time evolutions of multicharged In+ (n = 1-4) signals.

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.

Identifying the Multielectron Effect on Chemical Bond Rearrangement of CH3Cl Molecules in Strong Laser Fields

Strong field double ionization that triggers the chemical bond rearrangement of CH3Cl is investigated by impulsive control of the alignment of molecules. The alignment and laser intensity dependent H2+ and H3+ yields in linearly polarized femtosecond laser have been measured, and the obtained data show that the maximum signal of H2+ appears at the laser polarization parallel to the C-Cl axis of molecules and H3+ species are more likely to eject at the laser polarization parallel to the C-Cl axis at low laser intensity while the H3+ signal peaks at laser polarization perpendicular to the C-Cl axis at high laser intensity. The measurements indicate that electrons from HOMO - 1 and HOMO - 2 orbitals have been ionized for the generation of bond rearrangement at different laser intensity. Our results demonstrate the importance of multielectron effects and also provide an effective control method in the process of chemical bond rearrangement of the molecules in strong laser fields.

Contribution of resonance excitation on ionization of OCS molecules in strong laser field

Synopsis The resonant enhanced multiphoton ionization (REMPI) of OCS molecules has been studied by tracing the electron energy shift with the laser intensity dependent photoelectron energy spectra, we find two excited states ( 1 Δ and 1 Π) have been involved in the ionization of OCS at 800 nm and the REMPI through a certain excited state can be selectively controlled by varying the laser intensity. Furthermore, the REMPI of OCS through 4s Rydberg states at 400 nm laser fields has also been identified by angular distribution of electron.

Hn+ Ejection from Aligned CH3Cl Molecules in Intense fs Laser Fields

We report experimental results on strong-field laser interact with aligned CH3CI molecules, the ejection of fragments Hn+ dependent on alignment of CH3Cl molecules has been studied. The mechanism of fragmentation builds on the alignment sensitive ionization and dissociation from inner and outer valence orbitals or the excitation process of molecular have been discussed.

Tunneling Ionization of Aligned CH3X (X=I, Br, Cl) Molecules in Intense Femtosecond Laser Fields

We perform an experimental investigation on tunneling ionization of CH3X (X=I, Br, Cl) molecules in intense femtosecond laser fields (1013 to 1015 W/cm2). The angular distribution of the parent and fragment ions from the well aligned molecular targets has been measured. Compared with theoretical calculation, the results show some new insights into the ionization mechanism of these molecules in intense laser fields.

Multicenter effect in high-order above-threshold ionization of polyatomic molecules

The multicenter nature of molecules can affect the strong field ionization. By studying the resonancelike enhancement structure in the high-order ATI spectrum of C2H4 and C2H6, we illustrate how the multicenter effect contributes to the molecular tunneling ionization. We find the hydrogen contributions lead to the weak resonance-like structure of C2H6 but have no affect for C2H4, this target dependence origins from their different HOMO structures. Those conclusions are supported by Strong Field Approximation calculation.

Electron-Ion Differential Cross Section extracting from the High-order Above-Threshold Ionization spectroscopy of C2H4 and C2H6

We measured the angle-resolved High-order Above-Threshold Ionization spectroscopy of C2H4 and C2H6 with near-IR laser pulse, and extracted the electron-ion differential cross sections of those molecules from the electron spectroscopy by applying the quantitative rescattering theory. The differential cross sections show dramatically different distributions for C2H4 and C2H6, and this difference is believed to arouse from their different HOMO symmetry.