Evidence for excited electronic state interference in resonance raman scattering

The complex resonance Raman spectra of molecular bromine have been analyzed quantitatively and a clear demonstration of interference in the Raman intensity from the B(³11₀⁺_u) and ¹17_1u excited states has been found.     

The stimulated raman scattering process for possible use in photoselective isotope enrichment

The process of stimulated Raman scattering (SRS) is discussed as a means of achieving sizeable transient populations in the first vibrationally excited state of one species out of an isotopic mixture. This may be useful for photoselective isotope enrichment schemes. The main advantage of SRS excitation is the possibility of using one fixed-wavelength laser for the study of various compounds; also there is an inherent tendency to selectivity in SRS since the more abundant species in an isotopic mixture will show a higher gain for SRS. Sample calculations are presented showing Q-switched solid-state lasers to be good sources for selective excitation of gaseous mixtures, while mode-locked laser pulses are required for liquid samples.     

Determination of the spontaneous raman linewidth of CF4 by measurements of stimulated raman scattering in both transient and steady states

The spontaneous Raman linewith Δv of the v₁ mode of gaseous CF₄ is determined from 30 to 360 amagat by comparison of stimulated Raman scattering threshold intensity measurements performed with picosecond and nanosecond laser excitation. At high densities Δv = 0.20 cm^?1 is constant. A possible explanation of this effect is given in terms of collisional narrowing     

Resonance raman scattering in the region of a forbidden non-degenarate electronic state by a doubly degenerate vibration

It is shown that the resonance Raman scattering from a forbidden non-degenerate electronic state by a doubly degenerate mode depends strongly on Jahn—Teller interactions within an allowed doubly degenerate electronic state that lends its intensity to the scattering forbidden state.     

Laser-induced forward-transfer with light possessing orbital angular momentum

Helical light fields may carry both orbital angular and spin angular momentum which is respectively associated with their helical wavefronts (optical vortices) and rotating transverse electric fields. Interestingly, these helical light fields interact with materials and the orbital angular momentum of these fields can physically twist a range of materials, including metals, semiconductors, polymers, and liquids. With the aid of spin angular momentum, these fields can also form a range of helical structures. This light-matter interaction based on transfer of angular momentum has the potential to revolutionize industrial processes and enable technologies, such as advanced non-contact and nozzle-free printing. In this review paper, we focus on this printing technique, a process which we herein refer to as optical vortex laser induced forward transfer, and we show how it can be used for the production of next generation printed photonics/electronics/spintronics devices. Herein we review the interactions between the angular momentum of light and materials, and we discuss the ways in which optical vortices can be used to produce a variety of exotic structures. We also discuss the current state-of-the art of laser-induced forward-transfer technologies and detail some of the most novel devices, which have been fabricated using this optical vortex laser induced forward transfer, including hexagonal close-packed photonic-rings and plasmonic nanocores.     

Non-Aqueous surface-enhanced raman scattering spectra of benzene

Raman spectra of benzene at Ag electrode of electrochemical systems using alcohols as solvents were studied. Complicated potential dependence of benzene SERS band is attributed to competition between various adsorption states, the stability of which seems to depend on electrode potential and co-adsorption electrochemistry.     

Resonance raman scattering in molecules with vibronically coupled excited states

Resonance Raman excitation profiles and depolarization dispersion curves are studied for molecules with closely spaced electronic states coupled by nontotally symmetric vibrational coordinate.     

Symplectic integrators and the conservation of angular momentum

In this article we observe that generally symplectic integrators conserve angular momentum exactly, whereas nonsymplectic integrators do not. We show that this observation extends to multiple timesteps and to constrained dynamics. Both of these devices are important for efficient molecular dynamics simulations. © 1995 by John Wiley & Sons, Inc.     

The primitive L-pattern of angular momentum recoupling coefficients

Labarthes primitive L-patterns for the 3nj-symbols, where n=3,4,5,6,7, are reported. It is shown that, any L-patterns of the angular momentum recoupling coefficients can be expressed in terms of linear combinations of the primitive L-patterns and how the 3nj-symbols can be calculated from the expressions presented here.AMS subject classification: 81QShan-Tao Lai–Permanent Address for reprint requestYing-Nan ChiuAlso– Institute of Atomic and Molecular Sciences, Academia Sinica,Taipei, Taiwan, R.O.C.     

Liquid-crystalline ordering in polymeric networks as studied by polarized raman scattering

Uniaxially oriented polymer networks are produced by photoinitiated bulk polymerization of liquid-crystalline diacrylates. The order parameters S₂ and S₄ of the mesogenic moieties in these networks are simultaneously determined by means of the polarized Raman scattering technique. It yields an estimate of the orientation distribution function for different polymerization temperatures and for different lengths of the alkyl chain, present as a spacer in the liquid-crystalline diacrylate.     

Construction of orbital angular momentum eigenfunctions for many-particle systems by harmonic projection

Formulas are derived which allow the direct construction of total orbital angular momentum eigenfunctions for many-particle systems without the use of Clebsch–Gordan coefficients. One of the equations is closely analogous to Dirac' identity for the total spin operator. This equation describes the action of L² on a function of the particle coordinates in terms of a class operator of the symmetric group and a "contraction operator." A general projection operator for constructing symmetric eigenfunctions of L² is presented.     

Polarized raman scattering of highly oriented trans polyacetylene

Novel data on the polarization properties of the two resonantly enhanced Raman bands of trans polyacetylene have been obtained using the 609.6 nm line of a dye laser. Approximate corrections to take into account the optical anisotropy of the sample have been worked out. The changes of the observed band shapes and of the corrected intensities with the scattering configuration are consistent with a distribution of conjugation lengths. For short conjugated segments the electronic transition moment does not appear to be strictly aligned along the chain direction.     

Investigation of molecular orientation distributions by polarized raman scattering and polarized fluorescence

It is assumed that the intensity of the vibrational Raman scattering from each of the structural units (molecular segments or crystallites) in an oriented polymer solid is determined by a symmetric second-rank tensor. The distribution of orientations of the principle axes of the tensors is expanded in a series of generalized spherical harmonics, Z_lmn(θ)e^?imψe^?in?, and it is shown that relations among the coefficients in this expansion can be obtained from suitable intensity measurements using polarized radiation. If the orientation of the tensor axes within the structural unit is known (in the general case, for several Raman lines), then the coefficients M_lmn of a similar expansion for axes fixed in the units can be obtained for l, m, and n even and l ≤ 4. The limitation to even m follows from the assumption that the solid has at least orthotropic statistical symmetry but the limitations on n and l arise from the nature of the Raman effect. Some simple special cases are considered and some orientation-independent intensity sums are derived. It is shown that, with the simplifying assumption usually made, the theory of the polarized fluorescence method for determining molecular orientations is a special case of the theory for the Raman method.     

Non-Born-Oppenheimer variational calculations of HT+ bound states with zero angular momentum

We report fully nonadiabatic calculations of all rotationless bound states of HT+ molecular ion (t+p+e-) carried out in the framework of the variational method. We show that, in all the states, except the two highest ones, the bond in the system can be described as covalent. In the highest two states the bond becomes essentially ionic and HT+ can be described as a T+H+ complex. The wave function of the system was expanded in terms of spherically symmetric, explicitly correlated Gaussian functions with preexponential multipliers consisting of powers of the internuclear distance. Apart from the total energies of the states, we have calculated the expectation values of the t-p, t-e, and p-e interparticle distances, their squares, and the nucleus-nucleus correlation functions.     

Symmetrization of eigenfunctions of angular momentum in point groups

The eigenfunctions |jm〉 of angular momentum can combine linearly to make basis functions of irreducible representations of point groups. We surmount the projection operator and find a new method to calculate the combination coefficients. It is proven that these coefficients are components of eigenvectors of some hermitian matrices, and that for all pure rotation point groups, the coefficients can be made real numbers by properly choosing the azimuth angles of symmetry elements of point groups in the coordinate system. We apply the coupling theory of angular momentum to obtain the general formulas of the basis functions of point groups. By use of our formulas, we have calculated the basis functions with half‐integers j from 1/2 to 13/2 of double‐valued irreducible representations for the icosahedral group. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 83: 286–302, 2001     

Lifetime of reactive scattering resonances: Q-matrix analysis and angular momentum dependence for the F+H2 reaction by the hyperquantization algorithm

We report a study on the behavior with total angular momentum J of several resonances occurring at collision energies below or slightly above the reaction barrier in the F+H2-->HF+H reaction. Resonance positions and widths are extracted from exact time-independent quantum mechanical calculations using the hyperquantization algorithm and Smith's Q-matrix formalism which exploits complete S-matrix information. The results confirm previous work but provide much greater insight. Identification of quasi-bound states responsible for the resonances based on adiabatic models for the long-range atom-molecule interactions both in the entrance and exit channels, is successful except for the feature occurring at the lowest energy, which is found to overlap with an exit-channel resonance for J approximately 7. The two features are analyzed as overlapping resonances and their excellent Lorentzian fits, with well-behaved J-dependences of positions and widths, support the interpretation of the low-energy feature as a resonance to be associated to the triatomic transition state of the reaction. Resonance role on the reactive observables (integral cross sections and angular distributions) is investigated. The mechanism leading to forward scattering in the reactive differential cross section is commented, while the effects on rate constants, as well as the sensitivity of the resonance pattern to modification of the potential energy surface, are fully discussed elsewhere.     

Extension of total angular momentum representation in energy space

A previously developed representation of total angular momentum in energy space for three atomic systems is extended to include reactions of the type CF₃CN → CF₃ + CN. The effects of internal CF₃ rotation on the angular momentum constraint are shown under different conditions. The representation is used for comparison with recent infrared multiphoton dissociation experiments on this system.     

Two-dimensional stimulated resonance Raman spectroscopy of molecules with broadband x-ray pulses

Expressions for the two-dimensional stimulated x-ray Raman spectroscopy (2D-SXRS) signal obtained using attosecond x-ray pulses are derived. The 1D- and 2D-SXRS signals are calculated for trans-N-methyl acetamide (NMA) with broad bandwidth (181 as, 14.2 eV FWHM) pulses tuned to the oxygen and nitrogen K-edges. Crosspeaks in 2D signals reveal electronic Franck-Condon overlaps between valence orbitals and relaxed orbitals in the presence of the core-hole.     

Group theory approach for raman scattering of triatomic molecules

The symmetry of the rotation-vibration spectra for triatomic molecules is described by means of the group U(5). Group theory approach is adopted to give the transition matrix elements for calculation of the cross sections of vibrational and rotational Raman scattering. The results are in good agreement with the experimental values.