134 research outputs found
Chiral dichroism in bi-elliptical high-order harmonic generation
No full textThe application of strong bi-elliptically polarized laser fields to the generation of high-order harmonics in organic molecules offers exceptional opportunities for chiral recognition and chiral discrimination. These fields are made by combining an elliptically polarized fundamental, typically in the infrared range, with its counter-rotating second harmonic. Here we present a theoretical study of the harmonic emission from the chiral molecule propylene oxide in bi-elliptical fields. Our calculations include, for the first time in such a complex system, accurate photorecomination matrix elements, evaluated using the static-exchange density functional theory method. We show that bi-elliptical light can induce strong chiral dichroism in the harmonic spectra of chiral molecules in a broad range of harmonic numbers and ellipticities
Strong-field control and enhancement of chiral response in bi-elliptical high-order harmonic generation: An analytical model
No full textThe generation of high-order harmonics in a medium of chiral molecules driven by intense bi-elliptical laser fields can lead to strong chiroptical response in a broad range of harmonic numbers and ellipticities (Ayuso et al 2018 J. Phys. B: At. Mol. Opt. Phys. 51 06LT01). Here we present a comprehensive analytical model that can describe the most relevant features arising in the high-order harmonic spectra of chiral molecules driven by strong bi-elliptical fields. Our model recovers the physical picture underlying chiral high-order harmonic generation (HHG) based on ultrafast chiral hole motion and identifies the rotationally invariant molecular pseudoscalars responsible for chiral dynamics. Using the chiral molecule propylene oxide as an example, we show that one can control and enhance the chiral response in bi-elliptical HHG by tailoring the driving field, in particular by tuning its frequency, intensity and ellipticity, exploiting a suppression mechanism of achiral background based on the linear Stark effect
Grand-canonical quantized liquid density-functional theory in a Car-Parrinello implementation
No full textQuantized Liquid Density-Functional Theory (QLDFT) [S. Patchkovskii and T. Heine, Phys. Rev. E 80, 031603 (2009)], a method developed to assess the adsorption of gas molecules in porous nanomaterials, is reformulated within the grand canonical ensemble. With the grand potential it is possible to compare directly external and internal thermodynamic quantities. In our new implementation, the grand potential is minimized utilizing the Car-Parrinello approach and gives, in particular for low temperature simulations, a significant computational advantage over the original canonical approaches. The method is validated against original QLDFT, and applied to model potentials and graphite slit pores. \ua9 2013 AIP Publishing LLC.Peer reviewed: YesNRC publication: Ye
Ab initio investigation of potential energy curves of the 23 electronic states of IBr correlating to neutral 2P atoms
No full textPotential energy surfaces for all Born\u2013Oppenheimer electronic states of IBr molecule correlating to the neutral 2P (2P3/2 and 2P1/2) iodine and bromine are calculated for the first time. Electric dipole and polarizability curves (static and transition) are also determined. Calculations include scalar and spin\u2013orbit relativistic effects within all-electron Douglas-Kroll two-component Hamiltonian. Electron correlation is treated with quasi-degenerate multi-reference second-order perturbation theory. Seven adiabatic electronic states (X 1\u3a3+, A\u2032 3\u3a02, A 3\u3a01, 1 3\u3a00 12, B 3\u3a00+, B\u2032 3\u3a3 120+, and 2 3\u3a00+) exhibit significant covalent bonding, and can support vibrational states. Calculated spectroscopic parameters agree with experiment to better than 1000 cm 121 (Te), 10 cm 121 (\u3c9e), and 0.05 \uc5 (re). A new 1 3\u3a00 12 state correlating to ground-state atoms is predicted at Te 48 14 000 cm 121, \u3c9e 48 80 cm 121, and re 48 3.0 \uc5. The second new state (2 3\u3a00+) correlates to excited iodine atom, with Te 48 20 000 cm 121, \u3c9e 48 115 cm 121, and re 48 3.3 \uc5. Non-adiabatic coupling parameters are calculated for the four avoided crossings, which arise due to electronic spin\u2013orbit interaction. Estimated parameters of the B 3\u3a00+/B\u2032 3\u3a3 120+ crossing (Rc 48 3.32 \uc5; V 48 120 cm 121) agree with experimental values. The previously unsuspected 2 3\u3a00 12/1 1\u3a3 12 crossing of two repulsive surfaces provides a new collisional deactivation channel for Br* atoms at relative velocities above 1000 m s 121. Several repulsive states (including 1 1\u3a01 and 2 3\u3a01) intersect the B/B\u2032 system near the avoided crossing point, and may affect dynamics of IBr in strong laser fields.NRC publication: Ye
Nuclear Dynamics in Polyatomic Molecules and High-Order Harmonic Generation
No full textHigh-order harmonic generation in molecular gases is accompanied by short-time evolution of the nuclear vibrational wave function. Using normal coordinate representation, I derive a simple analytical theory of short-time autocorrelation functions and apply it to a test set of 15 small molecules. The results explain large isotope effects observed in CH4. At the harmonic cutoff in 800 nm driving field, nuclear dynamics reduces the emission intensity from NO and NO2 molecules by more than 50%. Autocorrelation functions are sensitive to the initial vibrational state, with the nodal structure of the initial vibrational wave packet reflected in the frequency spectrum of the harmonics.Peer reviewed: NoNRC publication: Ye
Towards understanding dynamics of atoms and molecules in intense laser fields
No full textIsolated atoms and molecules subjected to intense, long-wavelength laser fields undergo a number of processes, including ionization, fragmentation, and emission of high harmonics of the incident light. These processes can be used for a number of technological purposes (such as table-top coherent XUV and soft X-ray sources), and contain a rich body of information on the structure and dynamics of the parent molecules and their ions. I will describe the physical origin of these processes, and give some examples of their applications for strong-field spectroscopies. I will also briefly discuss some of the numerical techniques used for numerical simulations of electron dynamics in strong fields.Peer reviewed: YesNRC publication: Ye
Full-dimensional treatment of short-time vibronic dynamics in a molecular high-order-harmonic-generation process in methane
No full textWe present derivation and implementation of the multiconfigurational strong-field approximation with Gaussian nuclear wave packets (MC-SFA-GWP)\u2014a version of the molecular strong-field approximation which treats all electronic and nuclear degrees of freedom, including their correlations, quantum mechanically. The technique allows realistic simulation of high-order-harmonic emission in polyatomic molecules without invoking reduced-dimensionality models for the nuclear motion or the electronic structure. We use MC-SFA-GWP to model isotope effects in high-order-harmonic-generation (HHG) spectroscopy of methane. The HHG emission in this molecule transiently involves the strongly vibronically coupled 2F2 electronic state of the CH4+ cation. We show that the isotopic HHG ratio in methane contains signatures of (a) field-free vibronic dynamics at the conical intersection (CI); (b) resonant features in the recombination cross sections; (c) laser-driven bound-state dynamics; as well as (d) the well-known short-time Gaussian decay of the emission. We assign the intrinsic vibronic feature (a) to a relatively long-lived ( 654 fs) vibronic wave packet of the singly excited \u3bd4 (t2) and \u3bd2 (e) vibrational modes, strongly coupled to the components of the 2F2 electronic state. We demonstrate that these physical effects differ in their dependence on the wavelength, intensity, and duration of the driving pulse, allowing them to be disentangled. We thus show that HHG spectroscopy provides a versatile tool for exploring both conical intersections and resonant features in photorecombination matrix elements in the regime not easily accessible with other techniques.Peer reviewed: YesNRC publication: Ye
Thermodynamic stability of hydrogen clathrates
No full textThe stability of the recently characterized type II hydrogen clathrate [Mao, W. L., Mao, H.-K., Goncharov, A. F., Struzhkin, V. V., Guo, Q., et al. (2002) Science 297, 2247-2249] with respect to hydrogen occupancy is examined with a statistical mechanical model in conjunction with first-principles quantum chemistry calculations. It is found that the stability of the clathrate is mainly caused by dispersive interactions between H2 molecules and the water forming the cage walls. Theoretical analysis shows that both individual hydrogen molecules and nH2 guest clusters undergo essentially free rotations inside the clathrate cages. Calculations at the experimental conditions--2,000 bar (1 bar = 100 kPa) and 250 K confirm multiple occupancy of the clathrate cages with average occupations of 2.00 and 3.96 H2 molecules per D-5(12) (small) and H-5(12)6(4) (large) cage, respectively. The H2-H2O interactions also are responsible for the experimentally observed softening of the H[bond]H stretching modes. The clathrate is found to be thermodynamically stable at 25 bar and 150 K.NRC publication: Ye
- …
