Spectral researches on interaction of laser radiation with targets from titanium oxides

Spectral characteristics and kinetic processes of the laser-induced plasma used for the growth of films from titanium oxides were investigated. The experiments were carried out in vacuum, oxygen, and an oxygen radiofrequency discharge plasma and its afterglow. A collision-radiative model describing the state-to-state kinetics of titanium atoms and ions at various stages of flight of laser-induced plasma was proposed. It was shown that the conditions of local thermodynamic equilibrium are disturbed because of a fast gas-dynamic expansion of plasma. Nonetheless, the distribution functions of titanium atoms and ions over excited states are described by the Boltzmann formulas with different temperatures.     

On the determination of radiative lifetimes of excited Mn I and Mn II levels

Time-resolved laser-induced fluorescence spectroscopy has been used to measure the lifetimes of 46 Mn I and 7 Mn II levels. A high-current hollow cathode produces an effusive beam of manganese atoms and ions in the ground states and in metastable states. Selected states are populated with tunable dye laser pulses. The following fluorescence is measured by means of a Tektronix 1 GHz transient digitizer. Including the separately measured response function of the system in the evaluation procedure the full decay curve can be applied for a determination of the lifetimes. All measurements are performed with linearly polarized laser beams adjusted to the magic angle in order to exclude systematic error sources. A comparison with literature data is given.     

Radiative lifetimes of excited W I levels

Time-resolved laser-induced fluorescence spectroscopy has been used to measure the lifetimes of 47 selected W I levels with energies between 27800 and 48200 cm^?1. A high-current hollow cathode produces an effusive beam of tungsten atoms and ions in the ground states and in metastable states. Selected states are populated with tunable dye laser pulses. The subsequent fluorescence is measured by means of a Tektronix 1 GHz transient digitizer. By taking into account the separately measured response function of the system the lifetimes can be determined from the full decay curve. All measurements are performed with linearly polarized laser beams adjusted to the magic angle in order to exclude systematic error sources. The decay curves also have been inspected for quantum beats and for saturation effects. A comparison with the scarce literature data is given.     

Nanosecond time-resolved IR emission from molecules excited in a supersonic jet: intramolecular dynamics of NO2 near dissociation

IR emission from NO2 cooled in a supersonic jet and excited to a single, B 2B1 state rovibronic level at 22 994.92 cm(-1) above the ground-state zero point was detected with 10(-8)-s time resolution. The IR emission together with the laser-induced fluorescence decay measurement allows the deduction of the relaxation dynamics near the dissociation of NO2. Following the excitation this single rovibronic B 2B1 level decays on 1.0-s time scale primarily through electronic radiation. Collisions induce internal conversion with a rate constant of 3.0 x 10(7) Torr(-1) s(-1) to the mixed AX states. Collisions further induce internal conversion of the AX mixed states into highly vibrationally excited levels in the X states with a rate constant at least one order of magnitude slower. This mechanism results in the observation of a double-exponential decay in the laser-induced fluorescence and a rise in the IR emission intensity corresponding to the fast decay in the fluorescence intensity. The IR emission rate of the highly vibrationally excited X-state levels is estimated to be about one order of magnitude larger than the isoenergetic AX mixed states and much larger than the B 2B1 level, both with much less vibrational excitation.     

氯原子光诱导能级移动和增宽

应用半经典的微扰论方法计算出了氯原子光诱导能级移动和增宽,其大小与光强成正比光频率为41018 cm-1时,氯原子初态3p52P03/2和3p52P01/2在非共振情况下,光移动分别为67.6和26.9 MHz/Wμm-2.当激光频率v接近3p52P03/2→4s2P3/2的跃迁频率时,氯原子基态3p52P03/2的|MJ,MI〉=|-1/2,3/2〉→|1/2,3/2〉超精细ESR谱线发生近共振频率光移动,大小量级为0.1 MHz/Wμm-2,能级增宽一般远小于光移动     

The first observation of the rhodium monofluoride molecule: jet-cooled laser spectroscopic studies

Rhodium monofluoride has been observed and spectroscopically characterized. RhF molecules were produced under jet-cooled conditions in a laser vaporization molecular beam source by the reaction of a laser-vaporized rhodium plasma with SF(6) doped in helium, and studied with laser-induced fluorescence spectroscopy under both medium and high resolution. More than 25 bands have been observed in laser-induced fluorescence between 18,500 and 24,500 cm(-1) and five of these have been recorded at 200 MHz resolution. All bands of appreciable intensity have been rotationally analyzed. The ground electronic levels has Omega=2, which is attributed to an inverted (3)Pi state from the 2 delta(4)6 pi(3)12 sigma(1) electron configuration. The ground level rotational constants are B=0.272 45 cm(-1), D=1.035 x 10(-7) cm(-1). Very small ground level Lambda doublings are evident in the spectrum. Excited states having Omega=1, 2, and 3 have been identified. Dispersed fluorescence spectroscopy from 11 excited levels has been used to locate a large number of low-lying vibronic states within the energy range up to 8,000 cm(-1). A ground state vibrational interval of approximately 575 cm(-1) is suggested.     

Theory of laser-induced two-step electron-ion recombination

A theoretical framework for the quantitative interpretation of laser-induced electron-ion recombination is presented in terms of the density matrix taking into account stochastic bandwidth and pulse duration of the laser. The theory deals with recombination induced from the continuum into one group of states by one laser and further stabilized into a lower group of states by a second laser. Rate equations are then derived from the complete density matrix, and the conditions for their validity are discussed. Both density matrix and rate equations are applied to the interpretation of a recent experiment with equally good agreement.     

Analysis of relaxing laser-induced plasmas by absorption spectroscopy: Toward a new quantitative diagnostic technique

Broad-band near UV absorption spectroscopy was used to analyze atmospheric laser-induced plasmas formed on metallic and refractory targets. When the common emission spectroscopy only provides the density of the radiating atomic excited states, the technique reported in this paper is able to achieve high spatial resolution in the measurement of absolute number densities in expanding laser-induced plasmas. The reliability and the versatility of this technique, which is based on the comparison between results of the numerical integration of the radiative transfer equation and experimental spectra, were tested on different targets. The evolutions in time and space of the absolute population of the plasma species originating from metallic alloys (Al–Mg and Cu–Ni) and refractory materials (C/SiC) were achieved over large time scales. Owing to its accuracy, this absorption technique (that we call “LIPAS” for Laser Induced Plasma Absorption Spectroscopy) should bring a new and enhanced support to the validation of collisional-radiative models attempting to provide reliable evolutions of laser-induced plasmas.     

Heavy metal phosphate nanophases in silica: influence of radiolysis probed via f-electron state properties

We have assessed the feasibility of carrying out time- and wavelength-resolved laser-induced fluorescence measurements of radiation damage in glassy silica. The consequences of alpha decay of Es-253 in LaPO₄ nanophases embedded in silica were probed based on excitation of 5f states of Cm³⁺, Bk³⁺, and Es³⁺ ions. The recorded emission spectra and luminescence decays showed that alpha decay of Es-253 ejected Bk-249 decay daughter ions into the surrounding silica and created radiation damage within the LaPO₄ nanophases. This conclusion is consistent with predictions of an ion transport code commonly used to model ion implantation. Luminescence from the ⁶D_7/2 state of Cm³⁺was used as an internal standard. Ion-ion energy transfer dominated the dynamics of the observed emitting 5f states and strongly influenced the intensity of observed spectra. In appropriate sample materials, laser-induced fluorescence provides a powerful method for fundamental investigation of alpha-induced radiation damage in silica.     

Experimental and theoretical studies of the quenching of Li(3p,4p) by N2

Quenching mechanisms of the Li3p and Li4p states in collision with the nitrogen molecule are studied by laser-induced fluorescence spectroscopy and by a quantum chemical calculation. The Li3p state is observed to be efficiently quenched to the Li3s state detected as intense 3s-->2p emission. The Li4p state is efficiently quenched to the Li4s and Li3d states detected as 4s-2p and 3d-2p emissions, respectively. The potential-energy surfaces for the Li(2s-4p)N2 states show a large number of conical intersections and avoided crossings resulting from the couplings between the ionic [Li+(N2)-] and covalent configurations. There are a large number of stable excited states, and we give here the spectroscopic constants for the lowest two stable isomers correlating to Li2p+N2.     

Ultrafast photofragmentation dynamics of molecular iodine driven with timed XUV and near-infrared light pulses

Photofragmentation dynamics of molecular iodine was studied as a response to the joint illumination with femtosecond 800 nm near-infrared and 13 nm extreme ultraviolet (XUV) pulses delivered by the free-electron laser facility FLASH. The interaction of the molecular target with two light pulses of different wavelengths but comparable pulse energy elucidates a complex intertwined electronic and nuclear dynamics. To follow distinct pathways out of a multitude of reaction channels, the recoil of created ionic fragments is analyzed. The delayed XUV pulse provides a way of following molecular photodissociation of I(2) with a characteristic time-constant of (55 ± 10) fs after the laser-induced formation of antibonding states. A preceding XUV pulse, on the other hand, preferably creates a 4d(-1) inner-shell vacancy followed by the fast Auger cascade with a revealed characteristic time constant τ(A2)=(23±11) fs for the second Auger decay transition. Some fraction of molecular cationic states undergoes subsequent Coulomb explosion, and the evolution of the launched molecular wave packet on the repulsive Coulomb potential was accessed by the laser-induced postionization. A further unexpected photofragmentation channel, which relies on the collective action of XUV and laser fields, is attributed to a laser-promoted charge transfer transition in the exploding molecule.     

Laser-induced fluorescence studies of HfF+ produced by autoionization

Autoionization of Rydberg states of HfF, prepared using the optical-optical double resonance technique, holds promise to create HfF(+) in a particular Zeeman level of a rovibronic state for an electron electric dipole moment search. We characterize a vibronic band of Rydberg HfF at 54 cm(-1) above the lowest ionization threshold and directly probe the state of the ions formed from this vibronic band by performing laser-induced fluorescence on the ions. The Rydberg HfF molecules show a propensity to decay into only a few ion rotational states of a given parity and are found to preserve their orientation qualitatively upon autoionization. We show empirically that we can create 30% of the total ion yield in a particular ∣J(+), M(+) state and present a simplified model describing autoionization from a given Rydberg state that assumes no angular dynamics.     

Coherent control of indirect photofragmentation in the weak-field limit: control of transient fragment distributions

We demonstrate theoretically that laser-induced coherent quantum interference control of asymptotic states of dissociating molecules is possible--even in the (one-photon) weak-field limit starting from a single vibrational eigenstate--when resonances are in play. This is illustrated for the NaI molecule, where it is shown that the probability of observing atomic fragments as well as the distribution of their relative momenta can be changed by a phase modulated pulse with a fixed bandwidth. This type of control is restricted to finite times during the indirect fragmentation.     

Laser fluorescence spectrum of CuI. A re-interpretation

The laser-induced fluorescence spectrum of Cul is re-interpreted. The earlier assignment of the fluorescence doublets as P- and R-branch lines is correct but the assignment of the singlet series to superposition of P and R lines is incorrect. All observed lines in the fluorescence spectrum are explained in terms of transitions A ¹Π–X¹∑ and C¹∑–X¹∑. Vibrational and rotational constants of the upper states are determined.     

Homo- and heteronuclear alkali metal trimers formed on helium nanodroplets. Part I. Vibronic spectra simulations based on ab initio calculations

We compare the 3(4)A(1) and 4(4)B(2) states of homonuclear and heteronuclear alkali trimers formed of potassium and rubidium. The Multireference Rayleigh Schr?dinger Perturbation Theory of second order is applied to obtain the corresponding adiabatic potential energy surfaces. In the case of homonuclear trimers these pairs of states correspond to the two branches of the E?e Jahn-Teller distorted 2(4)E' state. For heteronuclear trimers, the vibrational modes Q(x) and Q(y) are no longer degenerate, but the two electronic states still show a conical intersection at obtuse (KRb(2)) or acute (K(2)Rb) isosceles geometries. Spectroscopic consequences of this situation are discussed, vibronic spectra are predicted and compared to laser-induced fluorescence spectra obtained in helium droplet isolation spectroscopy experiments of our group.     

Long radiative lifetimes of SO2 in a collision-free supersonic molecular beam

Radiative lifetimes and delayed laser-induced fluorescence spectra of cold SO₂ were measured in the range 3000–3150 Å in a differentially pumped collision-free supersonic beam. Lifetimes between 9 and 300 μs were obtained. We show the existence of high-density, low-intensity, and long-lifetime states in the vicinity of the strong spectral transitions.     

激光诱导荧光法测量PbS* A(0+)态的振动弛豫速率

The vibrational relaxation rates of PbS~*A(0~+) state in Ar and S_2 have been studied by laser-induced fluorescence technique. The vibrational relaxation rate of PbS~*A(0~+) in S_2 is two orders of magnitude larger than in Ar. Formation of unstable intermediate PbS_3 may be responsible for the fast relaxation. The energy transfer process between A(0~+)(V'=19) and B(1)(V'=6) states is also suggested.     

Conformational change in unsolvated Trp-cage protein probed by fluorescence

We report the first direct measurements of the unfolding of a protein, Trp-cage, in the gas phase using laser-induced fluorescence of protein ions in a heated quadrupole ion trap. The changes in enthalpy and entropy associated with the observed conformational change are obtained by fitting a two-state model of protein unfolding to the fluorescence intensities plotted versus temperature. The enthalpy and entropy changes for the 2+ and 3+ charge states are greater than the values measured in solution and depend on charge state.     

On chemical reactions in the laser-induced breakdown of a liquid

It is shown experimentally that a laser-induced breakdown of a liquid is accompanied by chemical reactions initiated by radicals and excited species formed in the spark. It is found that, in water, the laser-induced breakdown is accompanied by the dissociation of water and dissolved nitrogen molecules with the formation of HNO₂ and HNO₃, while, in a FeSO₄ aqueous solution, by the Fe²⁺ → Fe³⁺ oxidation reaction. It is assumed that the mechanism of the process is analogous to that of the action of ionizing radiations and the chemical action of ultrasonically induced cavitation (it is proposed that this mechanism of chemical action of a laser-induced spark proposed be termed indirect). Energy yields of these reactions are found to be of the same order of magnitude as for sonochemical redox reactions. It is shown that the laser-induced breakdown of an aqueous solution of maleic acid is accompanied by its stereoisomerization into fumaric acid, a process catalyzed by small amounts of an alkyl bromide. It is established that, for the formation of fumaric acid in a laser-induced spark, the energy yield is about five orders of magnitude higher than that typical of the above-mentioned redox reactions in the laser-induced spark.     

Analysis of the LIF Spectroscopy of Nickel Hydride in 19000-21400 cm-1

The laser-induced fluorescence (LIF) excitation spectrum of NiH was recorded in the spectral region from 15000 cm-1 to 21400 cm-1, with the NiH molecules produced by the reaction of sputtered nickel atoms with methanol under supersonic jet conditions. The 19000-21400 cm-1 portion of the spectrum of NiH is reported for the first time. Twenty-four bands were observed and classified into seven electronic transitions. Every band was rotationally analyzed. Higher vibrational levels of many excited states, A, B, D, E, F, and G,were observed and the complete set of spectroscopic parameters, vibrational frequency, unharmonic constant, rotational constant, and equilibrium length of these states were obtained. Some bands were reassigned