Intense interactions of molecules with a short-wavelength electromagnetic radiation field: I. The fundamentals of the nonadiabatic theory

The intense interactions between short-wavelength (SW) electromagnetic radiation with a wavelength λ ≥ 1 Å and intensity up to 10¹⁴ W/cm² and simple and polyatomic molecules are studied with the coherent excitations of high-lying Rydberg and autoionizing states taken into account. The Hamiltonian of a system “molecule + SW radiation” is obtained by using the methods of quantum electrodynamics. Conditions for the applicability of the dipole approximation to describe the interactions of molecules with radiation of the UV, VUV, XUV, and soft X-ray range are found. The fundamentals of the theory of resonance scattering of SW radiation from diatomic, triatomic, and symmetric-and asymmetric-top polyatomic molecules are outlined.     

Low-frequency spectroscopy of four-photon scattering of laser radiation in aqueous solutions of biopolymers

Four-photon scattering (FPS) spectroscopy is used to record rotational resonances of H₂O and H₂O₂ molecules in aqueous solutions of DNA and denatured DNA within a range of ±10 cm^-1 with a spectral resolution of 3 GHz. The resonance contribution of rotational transitions of these molecules in solutions was found to be considerably larger than that in distilled water. This fact is interpreted as a manifestation of the specific properties of a hydrate layer at the interface between water and DNA or denatured DNA molecules. An analysis of the FPS spectra shows that the concentration of H₂O₂ molecules in the hydrate layer of the DNA molecule increases threefold after denaturation. In addition, the FPS spectra of aqueous solutions of α-chymotrypsin protein with concentrations of 0-20 mg cm^-3 were measured in the spectral range of ±7 cm^-1. It is found that the velocity of hypersound in the protein aqueous solution, which is measured by the shift of the Mandelstam—Brillouin scattering spectrum components, is a cubic function of the concentration and reaches 3000 m/s at 20 mg/cm³.     

A comparison of Raman scattering,resonance Raman scattering,and fluorescence from molecules adsorbed on silver island films

The enhancement of Raman scattering (RS), resonance Raman scattering (RRS), and fluorescence from molecules adsorbed on silver-island films is reported. A heirarchy of enhancements is found: 10⁵ for RS, 10³ for RRS, and 0.1–10 for fluorescence, depending on the quantum yield of the free molecule. Using the framework of the electromagnetic theory of surface-enhanced Raman scattering, generalized to treat molecular resonance phenomena, we develop a unified picture of the role of the surface plasmon resonances, and the surface-induced damping, in the light scattering processes. The observed heirarchy of enhancements is shown to have important spectroscopic consequences.     

强场中NO分子回归谱的长程散射矩阵的理论研究

采用半经典散射矩阵方法研究外磁场中高里德伯态双原子分子在能量范围为77010—77050cm^-1的回归谱.通过引进模型势简化强磁场中NO分子的高里德伯电子的势函数,找出其在核转动量子数分别为N=1,3,5的三个通道中的闭合轨道,重点分析了强磁场中NO分子的长程散射矩阵元实部的傅里叶变换谱与闭合轨道之间的一一对应关系.     

Two-photon multiterm nonadiabatic transitions

The resonance Raman scattering phenomenon via the predissociated state is described in the four crossing terms A-(1, 2)-B model when terms 1 and 2 strongly interact. The Green's function closed representation for the coupled intermediate electronic terms 1 and 2 is obtained. The transition amplitude I _{A-(1, 2)-B} is found in the WKB approximation. The resonance Raman scattering via the predissociated ³Π_Ou ⁺ state of the interhalogen molecules is treated in detail.     

A novel electron scattering apparatus combining a laser photoelectron source and a triply differentially pumped supersonic beam target: characterization and results for the resonance

A novel electron scattering apparatus for high resolution studies of angle-differential elastic and inelastic electron scattering from atoms and molecules in the gas phase is described and its performance characterized. It combines a laser photoelectron source, a triply differentially pumped collimated supersonic beam target (half angle 0.015 rad, background to beam density ratio < 0.01), and several electron multipliers for simultaneous detection of elastically scattered electrons and metastable atoms (or molecules) due to inelastic scattering. In detailed test measurements of the yield for the production of metastable He^*(2³S₁) atoms around its threshold, the dependence of the overall energy width on various experimental parameters has been investigated. So far a resolution down to 7 meV (FWHM) has been obtained. Under such conditions we have investigated the profile of the He^- (1 s 2 s ^{2 2} S _1/2 ) resonance at the scattering angles 22 ^° , 45 ^° , and 90 ^° . From a consistent fit of the measured profiles by resonant scattering theory we determine a new value for the resonance energy ( E _r = 19.365(1) eV) and an accurate resonance width ( Γ = 11.2(5) meV). These results are consistent with the previously recommended values. Received 23 July 2002 Published online 29 October 2002 RID="a" ID="a"e-mail: hotop@physik.uni-kl.de RID="b" ID="b"Permanent address: Department of Physics and Astronomy, Drake University, Des Moines, IA 50311, USA.     

Infra red photodetachment threshold measurements: Li− and P−

Using gaseous sources of I₂ and HI containing the radioactive isotopes¹²⁴I and¹²⁶I effective cross sections for nuclear resonance scattering from the first 2⁺ states of¹²⁴Te and¹²⁶Te were measured. Information is obtained about the charging of the nonradioactive molecular partner afterEC decay, the interaction of highly charged ions with neutral molecules, and the slowing down of atoms in a Xe buffer gas. Indications of an iodine complex being stable in the gaseous phase are found.     

Nuclear resonance fluorescence in124Te and126Te: Vacancy cascades in molecules

Using gaseous sources of I₂ and HI containing the radioactive isotopes¹²⁴I and¹²⁶I effective cross sections for nuclear resonance scattering from the first 2⁺ states of¹²⁴Te and¹²⁶Te were measured. Information is obtained about the charging of the nonradioactive molecular partner afterEC decay, the interaction of highly charged ions with neutral molecules, and the slowing down of atoms in a Xe buffer gas. Indications of an iodine complex being stable in the gaseous phase are found.     

Scattering of atoms and molecules by an electromagnetic field

The scattering of atoms and molecules by the force of stimulated light pressure appearing in a standing wave is considered. It is shown that short (10^-8s) light pulses of tunable lasers can deviate resonance atoms through an angle of about 5°. A high selectivity of scattering is retained in a standing wave even in conditions of great saturation. Therefore the considered effect can be used for the separation of isotopes.     

Thermal neutron scattering parameters for light nuclei (A=12 to 27)

Neutron scattering lengths and free scattering cross sections were measured for isolated isotopes and natural elements in the mass region fromA=12 toA=27. By means of the Christiansen filter technique values for the coherent scattering lengths were obtained for the bound atoms of^12C,^13C,^14N,^15N,^16O,^17O,^18O, Mg and¹⁹F. Transmission experiments with neutrons of 0.51 meV, 1.26 eV and 5.19 eV yielded data for the free scattering cross sections of^19F,²³Na, Mg and¹⁹F. From all these results and with previous data the fundamental spin state scattering lengths for the concerned light nuclei have been deduced. The comparison of these values with resonance parameters has shown that the resonance data are complete. Therefore, values for the potential scattering radii could be obtained and discussed.     

Inverse kinematics resonance scattering on thick target with EXCYT beams

The resonance scattering method in inverse kinematics on infinite target has been applied to two systems, ¹⁸O + α and ⁹Be + α, in order to test and to optimize an experimental apparatus in view of a set of resonance scattering experiments to be performed with ⁸Li and ⁹Li radioactive ion beams delivered by the facility EXCYT. The scattering excitation functions, deduced for the two systems, were compared with previous results reported in literature. Results show that reliable stopping power data are essential for the application of this technique.     

Angular dependent rayleigh scattering of Mössbauer radiation on proteins

RSMR experiments with⁵⁷Fe radiation were performed on myoglobin. An areasensitive detector was employed for simultaneous angular dependent collection of the scattered quanta up to a maximum angle 2θ of 17‡. Experimental data of polycrystalline and lyophilized myoglobin are compared with computer calculations of the scattering which are based on the atomic coordinates determined by X-ray structure analysis. Special attention has been paid to the influence of coherence effects from collectively moving parts of the protein. A simple model is introduced in order to take into account these segmental motions. Our first results indicate that the sizes of collectively moving segments are comparable with spheres of about 6 å in diameter in dry myoglobin. In myoglobin crystals, where the molecules are surrounded by large hydration shells, the movements appear to be correlated in segments with sizes comparable to helices.

     

Study of nonlinear light scattering in water in the region of the second optical harmonic of laser radiation

The frequency-angular spectrum of nonlinear light scattering in water in the region of the second optical harmonic of picosecond Nd³⁺YAG laser radiation is studied. It is shown that this scattering occurs by the four-photon interaction mechanism. Statistical treatment of the spectra of four-photon scattering in the collinear interaction mode revealed a structure related to the frequency of infrared radiation caused by vibrations of cluster complexes of water molecules.     

Vibrational dynamics of fullerene molecules adsorbed on metal surfaces studied with synchrotron infrared radiation

Infrared (IR) spectroscopy of chemisorbed C₆₀ on Ag (111), Au (110) and Cu (100) reveals that a non-IR-active mode becomes active upon adsorption, and that its frequency shifts proportionally with the charge transferred from the metal to the molecule by about 5 cm^-1 per electron. The temperature dependence of the frequency and the width of this IR feature have also been followed for C₆₀/Cu (100) and were found to agree well with a weak anharmonic coupling (dephasing) to a low-frequency mode, which we suggest to be the frustrated translational mode of the adsorbed molecules. Additionally, the adsorption is accompanied by a broadband reflectance change, which is interpreted as due to the scattering of conduction electrons of the metal surface by the adsorbate. The reflectance change allows determination of the friction coefficient of the C₆₀ molecules, which results in rather small values (∼2×10⁹ s^-1 for Ag and Au, and ∼1.6×10⁹ s^-1for Cu), consistent with a marked metallic character of the adsorbed molecules. Pre-dosing of alkali atoms onto the metal substrates drastically changes the IR spectra recorded during subsequent C₆₀ deposition: anti-absorption bands, as well as an increase of the broadband reflectance, occur and are interpreted as due to strong electron–phonon coupling with induced surface states. Received: 6 June 2001 / Accepted: 23 October 2001 / Published online: 3 April 2002     

Relaxation experiments with synchrotron radiation

Relaxation phenomena show up in standard energy domain Mössbauer spectra via line broadening. The evaluation of such spectra is in most cases done by adopting the stochastic theory mainly developed in the 60s and 70s. Due to the time structure and the polarization of the synchrotron radiation nuclear resonance forward scattering in the time domain gives valuable information on relaxation mechanisms. We report here mainly on Nuclear Forward Scattering (NFS) experiments investigating the paramagnetic relaxation of the Fe³⁺ ion in (NH)₄Al_0.95 ⁵⁷Fe_0.05(SO₄)₂·12H₂O and briefly on recent investigations on charge fluctuations in Eu₃S₄.     

Resonances in an <Emphasis Type="Italic">S</Emphasis>-wave model of electron scattering off hydrogen-like ions

Irregularities in the cross section of electron scattering off hydrogen and hydrogen-like He⁺, Li⁺⁺, and Be⁺⁺⁺ ions are studied using an s-wave model. The resonance structure and irregularities in the scattering data are compared. A unified approach based on an exterior complex scaling method is used in performing calculations. The potential splitting approach is used for calculations of scattering in systems with asymptotic Coulomb interactions.     

Study of surface-molecule interactions using nuclear resonance photon scattering

Nuclear resonance photon scattering from the 6324-keV level in ¹⁵N was used for studying the surface-molecule interaction of nitrogen (N₂) on graphite. Other N-containing gaseous molecules (such as NO and N₂O) and other surfaces such that of activated carbon fiber (ACF) were also used. In particular, the average zero point energies of the out-of-plane vibrational and librational potentials of the molecules with respect to the adsorbing surfaces were determined. In addition, the out-of-plane orientation of the molecules versus T and as a function of the coverage were measured. In the nitrogen-graphite system, the results were used for testing the calculated in-plane and out of plane phonon spectra and for testing calculations of molecular dynamic simulations.     

Identification of two Ag‐2,2′:6′,2″‐terpyridine surface species on Ag nanoparticle surfaces by excitation wavelength dependence of SERS spectra and factor analysis: evidence for chemical mechanism contribution to SERS of Ag(0)–tpy

Measurement and interpretation of the excitation wavelength dependence of surface‐enhanced Raman scattering (SERS) spectra of molecules chemisorbed on plasmonic, e.g. Ag nanoparticle (NP) surfaces, are of principal importance for revealing the charge transfer (CT) mechanism contribution to the overall SERS enhancement. SERS spectra, their excitation wavelength dependence in the 445–780‐nm range and factor analysis (FA) were used for the identification of two Ag‐2,2′:6′,2″‐terpyridine (tpy) surface species, denoted Ag⁺–tpy and Ag(0)–tpy, on Ag NPs in systems with unmodified and/or purposefully modified Ag NPs originating from hydroxylamine hydrochloride‐reduced hydrosols. Ag⁺–tpy is a spectral analogue of [Ag(tpy)]⁺ complex cation, and its SERS shows virtually no excitation wavelength dependence. By contrast, SERS of Ag(0)–tpy surface complex generated upon chloride‐induced compact aggregate formation and/or in strongly reducing ambient shows a pronounced excitation wavelength dependence attributed to a CT resonance (the chemical mechanism) contribution to the overall SERS enhancement. Both the resonance (λ_exc = 532 nm) and off‐resonance (λ_exc = 780 nm) pure‐component spectra of Ag(0)–tpy obtained by FA are largely similar to surface‐enhanced resonance Raman scattering (λ_exc = 532 nm in resonance with singlet metal to ligand CT (¹ MLCT) transition) and SERS (λ_exc = 780 nm) spectra of [Fe(tpy)₂]²⁺ complex dication. Copyright © 2014 John Wiley & Sons, Ltd.     

Spin-dependent effects in inelastic scattering

The differential cross sections for the inelastic scattering of 10 MeV, 19.6 MeV, 30.4 MeV, 40 MeV and 49.35 MeV protons to the 2⁺ state (1.409 MeV) in ⁵⁴Fe and of 19.6 MeV protons to the 2⁺ state (0.846 MeV) in ⁵⁶Fe are analyzed in conjunction with the available data on the asymmetries and spin-flip probability amplitudes. The scattering amplitudes for both one step (valence plus core polarization) and two step (intermediate resonance) processes are evaluated using an antisymmetrized distorted wave approximation. Collective model representations for both the one step (core polarization) and two step (intermediate resonance) processes are used, and included are the effects of deforming the full Thomas spin-orbit potentials. The one step processes are fixed by the analyses of the scattering of 30.4, 40 and 49.35 MeV protons, with the core polarization contributions being constrained by the B(E2) values for the γ-ray deexcitation of the 2⁺ states. The analyses of the 19.6 MeV data demonstrates the need for an extra (two step) contribution to the reaction process and are consistent with the virtual formation of an L = 3 giant resonance. The 10 MeV data most certainly demonstrate compound nucleus effects but could also have some strength due to the virtual formation of an intermediate L = 2 giant resonance. The resonance parameters are consistent with recent information concerning the mass variation of giant resonances.