Single vibronic level fluorescence spectra from the S1(1B2u) state of p-difluorobenzene vapor

${}^1\text{B}{}_{\mathrm{2u}}\text{→}{}^1\text{A}{}_{\mathrm{1g}}$ fluorescence spectra have been obtained after pumping each of 19 bands in the S₁ ← S₀ absorption of p-difluorobenzene under collision-free conditions. The fluorescence analyses provide new assignments of some absorption bands and confirmations of others so that the assignment of the principal structure in absorption is essentially secure. Only the identity of some sequence forming modes remains unconfirmed. The assignments confirm a number of excited-state fundamentals and provide new values for others (Table I). Analysis of the weaker structure in zero-point S₁ fluorescence gives a full picture of vibrational activity in the S₁ ← S₀ transition. In so far as can be determined, the vibrational activities in fluorescence and absorption are in complete correspondence. The vibrational activity in the allowed p-difluorobenzene transition replicates to a good degree that found in the forbidden transition of benzene. Evidence suggesting a nonplanar S₁ state is found. A Franck-Condon analysis is given for progressions in three modes, and several strong Fermi resonances are identified in the S₁ state.     

Electron-impact excitation cross-sections for the3 S 0−,3 P 0−, and3 D 0-States of a ruthenium atom

The excitation cross-sections of transitions of a ruthenium atom from the³ S ⁰−,³ P ⁰−, and³ D ⁰-levels are measured by the method of extended crossed beams. Based on the results of measurements, the excitation cross-sections of the states are calculated (ignoring cascade contribution). Moscow Power Engineering Institute, 14, Krasnokazarmennaya St., Moscow, E-250, 111250, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 9–13, January–February, 1998.     

Underwater cytometer for in situ measurement of marine phytoplankton by a technique combining laser-induced fluorescence and laser Doppler velocimetry

We present a new type of flow cytometer that can operate underwater for a long time, as long as days, for measuring the size distribution, concentration, and biomass of marine phytoplankton. The major improvement of the instrument over existing techniques is the elimination of sample preparation, which is achieved with a laser Doppler crossed-beam arrangement for both defining a measurement volume and measuring the speed of the particle traversing it. By simultaneously sampling the laser-induced fluorescence signal and the Doppler signals, the technique can discriminate sizes of phytoplankton.     

Atomic fluorescence under monochromatic excitation: A level crossing experiment on the 6s6p 1P1 level of Ba I

A level crossing experiment on the 6s 6p ¹P₁ level of Ba I was performed using a narrow-band tunable dye laser and a strongly collimated atomic beam. The observed linewidth of the Hanle signal was minimally 45% of the width obtained with broad-band excitation.     

Simultaneous measurement of rotational and translational diffusion of anisotropic colloids with a new integrated setup for fluorescence recovery after photobleaching

This paper describes an integrated setup for fluorescence recovery after photobleaching (FRAP) for determining translational and rotational Brownian diffusion simultaneously, ensuring that these two quantities are measured under exactly the same conditions and at the same time in dynamic experiments. The setup is based on translational-FRAP with a fringe pattern of light for both the bleaching and monitoring of fluorescently labeled particles, and rotational-FRAP, which uses the polarization of a short bleach light pulse to create a polarization anisotropy. The fringe pattern of the probe beam is modulated in conjunction with a synchronized lock-in amplifier giving a fast, sensitive, ensemble-averaged measurement compared to microscope-image based techniques. The experimental polarization geometry we used ensures that the fluorescence emission is collected without polarization bias. Therefore, only the orientation of the absorption dipole moment of the fixed dye in the particles is measured, which simplifies interpretation of the data. The polarization is modulated rapidly between two orthogonal polarization states, giving the polarization anisotropy in one, single measurement. The rotational and translational Brownian diffusion of anisotropic colloids is measured for ellipsoids of revolution. This experiment shows that in this case the rotational correlation function matches a three-exponential decay in accordance with theoretical predictions.     

Growth, alloy formation and reaction with oxygen of Ag and Au submonolayers on W(1 1 0) studied by valence band and core level photoemission

We have studied epitaxial submonolayers of Ag and Au deposited one after another onto W(1 1 0) at room temperature and subsequently annealed at 600 K. Photoemission spectroscopy of valence bands and the Ag3d_5/2 core level has been used to monitor two-dimensional alloy formation. The extent of alloying depends on the order of deposition, composition and annealing. We have also studied the reaction of alloy surfaces to exposure of molecular oxygen at 300 and 600 K.     

Characteristic energy band values and electron attenuation length of a chemical-vapor-deposition diamond (0 0 1)2 × 1 surface

The characteristic energy band values such as the Fermi-level position with respect to valence band top for a boron-doped p-type hydrogen-terminated chemical-vapor-deposition (CVD) diamond (0 0 1)2 × 1 surface and for a clean CVD diamond (0 0 1)2 × 1 surface have been determined by a new method with an accuracy of ±0.02 eV. The electron attenuation length for the clean diamond (0 0 1)2 × 1 surface for the electron kinetic energy of C 1s X-ray photoemission peak by Mg Kα excitation is experimentally determined to be 2.1-2.2 nm. These values are compared and discussed with the previously reported experimental and simulation values.     

High-resolution measurements of pressure self-broadening and shift for the metyl-cyanide rotational J=1−0 line

Summary The capabilities of the travelling-wave spectrometry in the field of high-resolution measurements of low-pressure gases at microwave frequencies are discussed. Some details about the main aspects of the experimental procedure and the data management, useful for the improvement of overall performances, are specified. A pressure broadening of (72.5±1.5) MHz/Torr and a pressure shift of (4.3±0.3) MHz/Torr are measured for theJ=1−0 rotational line of CH₃C¹⁴N. These results are more accurate than those previously reported and in better agreement with the theoretical predictions.

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Riassunto Si discutono le prestazioni di uno spettrometro a microonde ad onda progressiva nel campo della spettroscopia ad alta risoluzione in gas a bassa pressione. Sono in particolare considerati alcuni aspetti delle procedure sperimentali e dell'elaborazionedei dati che hanno portato a decisi miglioramenti nella sensibilità e nelle prestazioni complessive dell'apparato sperimentale. Sono stati misurati per la riga rotazionaleJ=1–0 di CH₃C¹⁴N un coefficiente di autoallargamento per pressione di (72.5±1.5) MHz/Torr e uno shift di (4.3±0.3) MHz/Torr. Queste misure risultano piú accurate di quelle precedentemente riportate e in migliore accordo con le previsioni teoriche.

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Резюме Обсуждаются возможности использования микроволнового спектрометра со скользящей волной для измерений с высоким разрешением в газах при низких давлениях. Рассматриваются основные аспекты экспериментальной процедуры и обработки данных, которые позволяют улучшить чувствительность аппаратуры. Измерены величины самоуширения с давлением (72.5±1.5) МГц/Тор и сдвига с давлением (4.3±0.3) МГц/Тор для ротационной линииJ=1–0 для CH₃C¹⁴N. Полученные результаты являются более точными, чем ранее опубликованные, и лучше согласуются с теоретическими предесказаниями.

     

Laser excitation spectrum of PbO: Rotational analysis of the a(1)-X(0+) system

A flashlamp-pumped tunable dye laser has been used to investigate the a-X band system of PbO. Spectra with resolution adequate for rotational analysis were obtained by exciting a-X photoluminescence with the laser operating at a bandwidth of 0.2 cm^?1. The (3,1) and (4,1) bands have been rotationally analyzed, providing the rotational constants B₃ = 0.2389 ± 0.0002 cm^?1 and B₄ = 0.2374 ± 0.0002 cm^?1 for the a state. Observation of P, Q, and R branch structure confirms the assignment of the a state as a Hund's case (c), $\text{Ω}\text{= 1}$ state of PbO. Calculated combination defects having positive algebraic sign support the presence of a b(0^?) state approximately 350 cm^?1 above the a(1) state.     

CuPc molecules adsorbed on Au(1 1 0)-(1 × 2): growth morphology and evolution of valence band states

We present the growth morphology, the long-range ordering, and the evolution of the valence band electronic states of ultrathin films of copper phthalocyanine (CuPc) deposited on the Au(1 1 0)-(1 × 2) reconstructed surface, as a function of the organic molecule coverage. The low energy electron diffraction patterns present a (5 × 3) reconstruction from the early adsorption stages. High-resolution UV photoelectron spectroscopy data show the disappearance of the Au surface states related to the (1 × 2) reconstruction, and the presence of new electronic features related to the molecule-substrate interaction and to the CuPc molecular states. The CuPc highest occupied molecular orbital gradually emerges in the valence band, while the interface electronic states are quenched, upon increasing the coverage.     

SO2: High-resolution analysis of the (0 3 0), (1 0 1), (1 1 1), (0 0 2) and (2 0 1) vibrational states; determination of equilibrium rotational constants for sulfur dioxide and anharmonic vibrational constants

High resolution Fourier transform spectra of a sample of sulfur dioxide, enriched in ³⁴S (95.3%). were completely analyzed leading to a large set of assigned lines. The experimental levels derived from this set of transitions were fit to within their experimental uncertainties using Watson-type Hamiltonians. Precise band centers, rotational and centrifugal distortion constants were determined. The following band centers in cm⁻¹ were obtained: ν₀(3ν₂)=1538.720198(11), ν₀(ν₁ + ν₃)=2475.828004(29), ν₀(ν₁ + ν₂ + ν₃)=2982.118600(20), ν₀(2ν₃)=2679.800919(35), and ν₀(2ν₁ + ν₃)=3598.773915(38). The rotational constants obtained in this work have been fit together with the rotational constants of lower-lying vibrational states [W.J. Lafferty, J.-M. Flaud, R.L. Sams, EL Hadjiabib, J. Mol. Spectrosc. 252 (2008) 72-76] to obtain equilibrium constants as well as vibration-rotation constants. These equilibrium constants have been fit together with those of ³²S¹⁶O₂ [J.-M. Flaud, W.J. Lafferty, J. Mol. Spectrosc. 16 (1993) 396-402] leading to an improved equilibrium structure. Finally the observed band centers have been fit to obtain anharmonic rotational constants.     

Solvation and rotational relaxation of coumarin 153 in a new hydrophobic ionic liquid: An excitation wavelength dependence study

The solvent relaxation and rotational dynamics of coumarin 153 have been investigated in a new room temperature ionic liquid, 1-(2-methoxyethyl)-1-methylpyrrolidiniumtris(pentafluorethyl)trifluorophosphate [[MOEMPL][FAP]], at three different excitation wavelengths with a variation in temperature. Wavelength -dependent fluorescence decay behavior of the probe molecule in the present medium has been investigated by studying the time dependent fluorescence Stokes shift in the ps–ns time scale. The dynamic fluorescence Stokes shift measurements suggest that the time-resolvable part of the solvation dynamics is biphasic in nature and the average solvation time depends on the excitation wavelengths. Rotational coupling constants, obtained from the time- resolved anisotropy data, indicate no specific interaction between the probe molecule and the ionic liquids. The excitation wavelength dependent solvation dynamics is attributed to the heterogeneous nature of the present ionic liquid.     

Postcollision interaction upon electron excitation of the 5sns 1 S 0 and 5snd 3 D j levels of the cadmium atom

The optical excitation functions (OEFs) for two series of spectral lines of the Cd atom originating from the 5sns ¹ S ₀ (n = 6?11) and 5snd ³ D _{1, 2, 3} (n = 5 and 6) levels excited by an ultramonoenergetic (ΔE _1/2 < 0.05 eV) electron beam with energies exceeding the single ionization threshold are presented. In the energy range from 10.8 to 12.9 eV, the energy dependences of the excitation cross sections of the studied spectral transitions exhibit the effect of postcollision interaction of slow scattered and fast emitted electrons. This process leads to an additional population of the initial levels of the spectral transitions due to the capture of a scattered electron into an excited atomic level. The energies and widths of the electronic decay of autoionizing states are estimated in the classical approach by two methods, namely, by the least squares method and by direct calculation. Calculations are performed using approximate formulas valid for different relations between the postcollision shifts of the OEF maxima and the binding energies of the atomic levels. The terms of the autoionizing atomic states responsible for the maxima observed in the OEFs of the spectral transitions are determined.     

LIF excitation spectra for S0 → S1 transition of anthranilic acid: Detailed studies

Laser-induced fluorescence (LIF) excitation spectra of jet-cooled molecules of anthranilic acid were investigated. In order to distinguish bands belonging to the monomer from those belonging to the dimer species three different spectra were recorded under conditions which differed in the value of partial pressure of vapours of anthranilic acid. Narrow bandwidth of rotational profiles in the acquired spectra made it possible to resolve new interesting spectral features and to analyse the rather small anharmonicity in progressions of several low-frequency vibrations. Eleven fundamental bands up to ca. 1400 cm⁻¹ and five overtones of out-of-plane vibrations were assigned. Simulation based on approximate relations of the experimental band intensities of overtones and combination bands with respect to fundamental bands was carried out. This simulation was found a simple and practical tool in analysis of the spectra and an aid to verify the proposed assignment.Harmonic and anharmonic frequencies of vibrational modes were calculated using the HF/6-31G∗∗ and CIS/6-31G∗∗ methods for the S₀ and S₁ state, respectively. Modelling of band intensities using displacement parameters derived from the results of the ab initio calculations was performed. This modelling significantly underestimates the displacement parameters. The Dushinsky matrix derived from the results of the ab initio calculations was used to check the validity of the models and to find modes which undergo large frequency changes and mode mixing upon electronic excitation.     

The Nernst-Ettingshausen coefficient in conductors with a narrow conduction band: Analysis and application of its results to HTSC materials

A theoretical analysis is made of the Nernst-Ettingshausen coefficient Q for the case of a narrow conduction band present in the band spectrum of a material. It is shown that the presence of such a band results in a qualitative change in the mechanism responsible for the Nernst-Ettingshausen effect as compared to the classical case of a broad conduction band and that the behavior of this coefficient reveals a number of specific features that are different from the case of the classical theory of transport coefficients in semiconductors and metals. It is demonstrated that the pattern of the Q(T) relation in the case of a narrow band is drastically affected by the asymmetry of the dispersion curve, whereas the other features of the band spectrum and of the properties of the carrier system, including the character of the energy dependence of the relaxation time, are less significant and, in a first approximation, can be disregarded. The calculated Q(T) curves are in qualitative agreement with the experimental relationships obtained for doped HTSCs of the YBa₂Cu₃O_y system. The possibility of using this approach for a complex analysis of the experimental temperature dependences of the four transport coefficients in the normal phase of HTSC materials is demonstrated.     

Dissociative chemisorption of H2 on Pt(1 1 1): isotope effect and effects of the rotational distribution and energy dispersion

Six-dimensional quantum dynamics calculations on dissociative scattering of H₂ and D₂ from Pt(1 1 1) are performed. The six-dimensional potential energy surface used was generated using density functional theory employing the generalized gradient approximation. The isotope effect, the effect of widening the rotational distribution on the dissociation probability and the effect of the energy dispersion are investigated, as they are possible reasons for a discrepancy between previous theoretical work and molecular beam experiments. It was found that these effects cannot explain the differences between the theoretical and experimental results.     

The A2Σ+-X2Πi electronic band system of the OD free radical: Spectroscopic data for the 0-0 sequence,and rotational term values for A2Σ+ and X2Πi

The A²Σ⁺-X²Π_i emission system of the OD radical has been recorded at high resolution from a discharge through flowing D₂O at 0.1 torr pressure. The 0-0, 1-1, and 2-2 bands of the Δv = 0 sequence have been analyzed in detail for the first time. A table of the vacuum wavenumbers and wavelengths in air of the rotational lines of these bands is presented, together with some additional measurements for the 0–1 band. The data are used to obtain a self-consistent set of term values for v′ and v″ = 0, 1, which reproduces the observed line frequencies with an average deviation of less than 0.02 cm^?1. Earlier, lower resolution data for bands with v′ and v″ = 2, 3 are also combined with the present measurements to give approximate term values for these higher levels.