Probe Beam Dichroism and Birefringence in Stumulated Raman Scattering of Biologically Relevant Polyatomic Molecules

The dichroism and birefringence effects in stumulated Raman scattering (SRS) in polyatomic molecules were studied theoretically. General expressions have been derived describing the change of the intensity and polarization of the probe pulse after transmission through a solution of arbitrary polyatomic molecules for any initial polarization of each of the laser pulses. The expressions were written in terms of spherical tensor operators that allowed for separation of the both beams polarization matrices and the material part containing three scalar values of nonlinear optical susceptibility where that rank K is limited to the values K=0,1,2. The expressions are valid for arbitrary directions of propagation of both pump and Stokes light beams and arbitrary polarizations of both beams. The expressions contain contributions from linear dichroism and birefringence in the molecular excited states. It was shown that, under certain conditions, both effects can be observed simultaneously. The geometry of almost collinear propagation of the pump and Stokes pulse beams through the molecular sample was considered, and it was shown that the contributions from linear dichroism and birefringence to the signal can be completely separated in the experiment by means of an appropriate choice of a probe beam polarization analyzer placed in front of the photodetector. The expressions obtained were used to describe the signals obtained using the polarization-modulation technique developed recently by the authors (Gorbunova et al, Phys. Chem. Chem. Phys. 2020, Vol. 22, 18155-18168). It was shown that the modulated dichroism and birefringence signals could be observed in quadrature to the second harmonic of the modulated reference signal.Comment: 11 pages, 2 figure

Anisotropic relaxation in NADH excited states studied by polarization-modulation pump-probe transient spectroscopy

We present the results of experimental and theoretical studies of fast anisotropic relaxation and rotational diffusion in the first electron excited state of biological coenzyme NADH in water-ethanol solutions. The experiments have been carried out by means of a novel polarization-modulation transient method and fluorescence polarization spectroscopy. For interpretation of the experimental results a model of the anisotropic relaxation in terms of scalar and vector properties of transition dipole moments and based on the Born-Oppenheimer approximation has been developed. The results obtained suggest that the dynamics of anisotropic rovibronic relaxation in NADH under excitation with 100~fs pump laser pulses can be characterised by a single vibration relaxation time $\tau_v$ laying in the range 2--15~ps and a single rotation diffusion time $\tau_r$ laying in the range 100--450~ps a subject of ethanol concentration. The dependence of the times $\tau_v$ and $\tau_r$ on the solution polarity (static permittivity) and viscosity has been determined and analyzed. Limiting values of an important parameter $\langle P_2(\cos\theta(t))\rangle$ describing the rotation of the transition dipole moment in the course of vibrational relaxation has been determined from experiment as function of the ethanol concentration and analyzed.Comment: 14 pages, 13 figure

Polarization of molecular angular momentum in the chemical reactions Li + HF and F + HD

The quantum mechanical approach to vector correlation of angular momentum orientation and alignment in chemical reactions [G. Balint-Kurti and O. S. Vasyutinskii, J. Phys. Chem. A 113, 14281 (2009)]10.1021/jp902796v is applied to the molecular reagents and products of the Li + HF [L. Gonzalez-Sanchez, O. S. Vasyutinskii, A. Zanchet, C. Sanz-Sanz, and O. Roncero, Phys. Chem. Chem. Phys. 13, 13656 (2011)]10.1039/c0cp02452j and F + HD [D. De Fazio, J. Lucas, V. Aquilanti, and S. Cavalli, Phys. Chem. Chem. Phys. 13, 8571 (2011)]10.1039/ c0cp02738c reactions for which accurate scattering information has become recently available through time-dependent and time-independent approaches. Application of the theory to two important particular cases of the reactive collisions has been considered: (i) the influence of the angular momentum polarization of reactants in the entrance channel on the spatial distribution of the products in the exit channel and (ii) angular momentum polarization of the products of the reaction between unpolarized reactants. In the former case, the role of the angular momentum alignment of the reactants is shown to be large, particularly when the angular momentum is perpendicular to the reaction scattering plane. In the latter case, the orientation and alignment of the product angular momentum was found to be significant and strongly dependent on the scattering angle. The calculation also reveals significant differences between the vector correlation properties of the two reactions under study which are due to difference in the reaction mechanisms. In the case of F + HD reaction, the branching ratio between HF and DF production points out interest in the insight gained into the detailed dynamics, when information is available either from exact quantum mechanical calculations or from especially designed experiments. Also, the geometrical arrangement for the experimental determination of the product angular momentum orientation and alignment based on a compact and convenient spherical tensor expression for the intensity of the resonance enhanced multiphoton ionization (REMPI 2 + 1) signal is suggested. © 2013 AIP Publishing LLC.O.R. acknowledges financial support from the Spanish Ministery de Ciencia e Innovación under Grant Nos. CSD2009-00038 and FIS2010-18132, and by Comunidad Autónoma de Madrid (CAM) under Grant No. S-2009/MAT/1467.Peer Reviewe

Fragmentation of uracil after electron capture by doubly charged ions

Single electron capture from molecular uracil (C4H4N2O2) by doubly-charged He2+, C2+, and O2+ atomic ions followed by the fragmentation of uracil ions has been studied using time-of-flight mass-spectrometry at the collision velocity range 0.13–0.65 a.u. The uracil ion fragmentation mechanism has been clarified by the arrival time correlation analysis for all ion-fragments produced in a single collision. Electron capture with ionization cross section has been determined from experiment. As shown, single electron capture in reaction of uracil with C2+ leads to high fragmentation probability of the resulting uracil ion. The role of electron core rearrangement in the C2+ and O2+ atomic ions is discussed

O(1D2^1D_2) ORBITAL ORIENTATION IN THE ULTRAVIOLET PHOTODISSOCIATION OF OZONE

Author Institution: Department of Chemistry, Wayne State Univeristy, Detroit MI 48202, USA, Department of Chemistry, Stony Brook University, Stony Brook, NY 11794, USA; Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, ON, K1A 0R6, Canada; Ioffe Physico-technical Institute, Russian Academy of Sciences, 194021 St. Petersburg, RussiaWe present the absolute velocity-dependent orbital orientation for O($^1D_2$) atoms produced from the photodissociation of ozone in the 248-285 nm region obtained using the DC slice imaging method. The results are analyzed in terms of laboratory frame anisotropy parameters describing distinct excitation and dissociation mechanisms possessing characteristic angular distributions. The results show negligible orbital orientation produced in dissociation by circularly polarized light, but strong recoil speed-dependent orientation following photolysis by linearly polarized light at all wavelengths studied. The origin of this polarization is ascribed to nonadiabatic transitions at avoided crossings and at long range