High-order harmonic generation from polyatomic molecules including nuclear motion and a nuclear modes analysis

We present a generic approach for treating the effect of nuclear motion in the high-order harmonic generation from polyatomic molecules. Our procedure relies on a separation of nuclear and electron dynamics where we account for the electronic part using the Lewenstein model and nuclear motion enters as a nuclear correlation function. We express the nuclear correlation function in terms of Franck-Condon factors which allows us to decompose nuclear motion into modes and identify the modes that are dominant in the high-order harmonic generation process. We show results for the isotopes CH$_4$ and CD$_4$ and thereby provide direct theoretical support for a recent experiment [Baker {\it et al.}, Science {\bf 312}, 424 (2006)] that uses high-order harmonic generation to probe the ultra-fast structural nuclear rearrangement of ionized methane.Comment: 6 pages, 6 figure

Ionization of oriented targets by intense circularly polarized laser pulses: Imprints of orbital angular nodes in the 2D momentum distribution

We solve the three-dimensional time-dependent Schr\"{o}dinger equation for a few-cycle circularly polarized femtosecond laser pulse interacting with an oriented target exemplified by an Argon atom, initially in a $3\text{p}_{x}$ or $3\text{p}_{y}$ state. The photoelectron momentum distributions show distinct signatures of the orbital structure of the initial state as well as the carrier-envelope phase of the applied pulse. Our \textit{ab initio} results are compared with results obtained using the length-gauge strong-field approximation, which allows for a clear interpretation of the results in terms of classical physics. Furthermore, we show that ionization by a circularly polarized pulse completely maps out the angular nodal structure of the initial state, thus providing a potential tool for studying orbital symmetry in individual systems or during chemical reactions

Effect of salinity, nitrogen and phosphorus stresses on growth and photosynthetic activity of the marine microalga Dunaliella parva

The growth of the marine green alga Dunaliella parva was studied and optimized under different salinity levels of NaCl (0.5, 1, 2, 2.5, and 3.5 M). The growth was monitored by cell number pigment content (Chl. a, Chl. b, and carotenoids). The grown alga, under the optimal conditions, was exposed to different stresses (nitrogen, phosphorus starvation, and salinity either singly or combined. Under nitrogen and phosphorus starvation, either singly or combined, the growth rate and the metabolic activities were decreased. Under salt stress (2.5 M NaCl) combined with N starvation and heavy metals stress, glycerol production increased, while glycerol synthesis decreased under salt stress of 1 M NaCl and P starvation. Also, free radicals (total antioxidant, reducing power, DPPH, and Lipid peroxidation), pigment content, and activity of antioxidant enzymes were recorded. D. parva grown under salinity level (2.5 M NaCl) combined with nutrient starvation correlated with more efficient enzymatic antioxidant activity accumulation. This study strongly suggested that the induction of antioxidant defense was one component of the tolerance mechanism of D. parva to salinity, as evidenced by its growth behavior

Ionization of 1D and 3D oriented asymmetric top molecules by intense circularly polarized femtosecond laser pulses

We present a combined experimental and theoretical study on strong-field ionization of a three-dimensionally oriented asymmetric top molecule, benzonitrile (C$_7$H$_5$N), by circularly polarized, nonresonant femtosecond laser pulses. Prior to the interaction with the strong field, the molecules are quantum-state selected using a deflector, and 3-dimensionally (3D) aligned and oriented adiabatically using an elliptically polarized laser pulse in combination with a static electric field. A characteristic splitting in the molecular frame photoelectron momentum distribution reveals the position of the nodal planes of the molecular orbitals from which ionization occurs. The experimental results are supported by a theoretical tunneling model that includes and quantifies the splitting in the momentum distribution. The focus of the present article is to understand strong-field ionization from 3D-oriented asymmetric top molecules, in particular the suppression of electron emission in nodal planes of molecular orbitals. In the preceding article [Dimitrovski et al., Phys. Rev. A 83, 023405 (2011)] the focus is to understand the strong-field ionization of one-dimensionally-oriented polar molecules, in particular asymmetries in the emission direction of the photoelectrons.Comment: 12 pages, 9 figure