共查询到20条相似文献,搜索用时 15 毫秒
1.
分子量子态的研究,特别是分子激发态演化过程的研究不仅可以了解分子量子态的基本特性和量子态之间的相互作用,而且可以了解化学反应过程和反应通道间的相互作用.飞秒时间分辨质谱和光电子影像是将飞秒抽运-探测分别与飞行时间质谱和光电子影像相结合的超快谱学方法,为实现分子内部量子态探测,研究分子量子态相互作用及超快动力学过程提供了强有力的工具,可以在飞秒时间尺度下研究单分子反应过程中的光物理或光化学机理.本文详细介绍了飞秒时间分辨质谱和光电子影像的技术原理,并结合本课题组的工作,展示了这两种方法在量子态探测及相互作用研究领域,特别是激发态电子退相、波包演化、能量转移、分子光解动力学以及分子激发态结构动力学研究中的广泛应用.最后,对该技术的发展前景以及进一步的研究工作和方向进行了展望. 相似文献
2.
The low-temperature dynamics of two different varieties of a low-molecular glass—protonated toluene (C6H5CH3) and perdeuterated toluene (C6D5CD3)—weakly doped with tetra-tert-butylterrylene (TBT) molecules was investigated with single-molecule spectroscopy. In both glassy matrices the distributions of the spectral widths were measured for a large number of single TBT molecules at T=2 K. The marked shift of the distribution upon deuteration of matrix was observed and attributed to an isotope effect which is qualitatively analyzed. It was found that at this temperature the tunneling dynamics of the matrix dominates the broadening behavior and hydrogen/deuterium atoms are involved in the tunneling motions. 相似文献
3.
Theoretical Study of the Influence of Femtosecond Laser Wavelength on the Evolution of a Double-Minimum Electronic Excited State Wave Packet for NaRb
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Employing the two-state model and the time-dependent wave packet method, the influence of femtosecond laser wavelength on the evolution of the double-minimum electronic excited state wave packet is numerically investigated. For different laser wavelengths, evolutions of the double-minimum electronic excited state wave packet with time and internuclear distance are different. One can control the evolution of the wave packet by varying the laser wavelength appropriately, which will benefit the light manipulation of atomic and molecular processes. Furthermore, study of the dynamics of the NaRb molecule may yield clues to creating an ultracold molecule. 相似文献
4.
Krishnendu Kundu 《Molecular physics》2014,112(11):1577-1588
The role of low-lying excited states on the spin–lattice relaxation times (T1) of organic radicals has been investigated. To test the applicability of Kivelson's electric field fluctuation model (D. Kivelson, J. Chem. Phys. 45, 1324 (1966)), based on the Orbach mechanism of spin relaxation, the T1s of the anion radicals of benzene, benzene-1-d, toluene, ethyl benzene, isopropyl benzene, t-butyl benzene, p-xylene, 1,2,4-trimethyl benzene and 1,3,5-trimethyl benzene in liquid solutions, with potassium cation as the counter ion, have been measured by the pulse saturation recovery technique. The energy gap between the ground and the first excited electronic states changed with the substitutions to different extent. The spin–lattice relaxation rates showed correlation with this energy gap. Anion radicals of benzene and benzene-1-d showed the shortest T1 among the radicals studied here. A small but measurable energy splitting due to the deuterium substitution in benzene-1-d radical was obtained from the temperature dependence of T1. Spin–lattice relaxation times of benzene anion measured here decreased monotonically in the range of ?60 to ?125 °C, in contrast to some reported claims of very unusual temperature dependence, based on the continuous wave microwave power saturation studies. Our results also showed that the ion pairing between benzene anion and potassium cation did not significantly influence the spin–lattice relaxation times. 相似文献
5.
The de-excitation process of FA(type I) centers in KCl:Na has been investigated by measuring the hot luminescence spectrum from optically excited FA centers with time-resolved spectroscopy. The experimental results are analyzed by using a model that describes a time evolution of the phonon wave packet during the vibronic relaxation process from the Franck-Condon state to a relaxed excited state. From the analysis of the experimental data, information on the vibronic mixing between 2p and 2s states, whose magnitude varies during the relaxation process, and the adiabatic potential energy curves of 2s and 2p states are extracted. The present results are compared with the already known ones of the FA(type II) centers. 相似文献
6.
We extend a method proposed by Seidner et al. [J. Chem. Phys. 103, 3998 (1995)] to extract directional terms from a time-dependent molecular polarization to obtain time-resolved four-wave-mixing
(FWM) signals. Instead of employing perturbation theory, the total polarization induced in the molecular sample by the interaction
with several femtosecond laser pulses is determined by solving the time-dependent Schr?dinger equation for the nuclear dynamics
in coupled electronic states numerically exact. Repeating the calculation for several combinations of relative phases of the
involved fields leads to a linear system of equations for the contributions emitted in different directions. Gas-phase I2 molecules serve as a numerical example.
Received: 22 September 1999 / Published online: 30 June 2000 相似文献
7.
We explain the polarization dependence of four wave mixing (FWM) quantum beats for semiconductors as essentially due to the spin phase correlations of photo-excited electrons, rather than to Coulomb interaction between the electrons. A theoretical analysis is given within the framework of optical Bloch equations for the light–semiconductor interactions and the Luttinger–Kohn model for the band structure. Residual Coulomb interactions between charge carriers are ignored. The results suggest that the polarization dependence of FWM quantum beats is a purely coherent effect of dual photon excitations, rather than, e.g., exciton–exciton Coulomb interaction. We show that the coherence transfer between the excited states is responsible for the FWM in a configuration with orthogonally polarized pump and probe. 相似文献
8.
H. Hess K.R. Asmis T. Leisner L. Wöste 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):145-149
We present results on the ultrafast dynamics of mass-selected neutral Ag4 clusters using NeNePo (negative ion - neutral - positive ion) femtosecond pump-probe spectroscopy. One-color pump-probe spectra
of the Ag4
-/Ag4/Ag4
+ system measured at 385 nm and an internal cluster temperature of 20 K display a complex beat structure over more than 60
ps. The oscillatory structure is attributed to vibrational wave packet dynamics in an excited “dark" state of neutral Ag4. A dominant 740 fs wave packet period as well as wave packet dephasing and rephasing are observed in the spectra. Fourier
analysis of the spectra yields a group of frequencies centered around 45 cm-1 and an anharmonicity χ
e2νχ
eχ
e of 2.65 cm-1 for the active vibrational mode.
Received 30 November 2000 相似文献
9.
A. A. Makarov 《Hyperfine Interactions》1987,38(1-4):599-624
Generally, the subject of the paper is related to the structure of highly excited vibrational states of polyatomic molecules.
The problem is treated in terms of intramolecular vibrational dynamics as well as spectroscopy of vibrational transitions.
Theoretical approximations which allow us to calculate spectra starting from dynamics are discussed. A microscopic treatment
of spectroscopic relaxation timesT
1 andT
2 is given. Also, various experimental approaches to study the problem are outlined including the measurements of stochasticity
onset in molecules. 相似文献
10.
The Liouville formalism in frequency space is used in the present study to investigate the effect of the intramolecular coupling on the four wave mixing signal (FWM) of a two-level system. The internal rovibrational structure is incorporated by including the spin-orbit residual interaction in the total Hamiltonian of the system. The behavior of the FWM signal as a function of the coupling parameters (v and V0) has been studied. The main properties affected were the permanent and transition dipole moments of the solute molecules when the rotating wave approximation is neglected. Reduced polarization expressions are obtained from the resonant terms and from the larger coherence and population density contributions to the macroscopic polarization, which in turn allows us to characterize individual resonances in the resulting frequency spectrum. 相似文献
11.
S. Rutz E. Schreiber 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(2):151-158
For the first time, the femtosecond real-time vibrational dynamics of the rare 41,41K2 isotope, excited to the electronic state, could be selectively studied by means of time-resolved three photon ionization. A vibrational period of fs is determined. Superimposed, a beat structure with a period of 20 ps is observed. A detailed Fourier analysis reveals a
strong band of three lines centered around 65.5 cm-1. A significant perturbation of the wave packet caused by spin-orbit coupling of the A and the crossing state is found. This perturbation is the reason for the fast dephasing of the initially generated wave packet within about
10 ps. The spectrogram of the real-time data shows total revivals of the wave packet at 20 ps and 40 ps. Fractional revivals
are found for times around 10 ps and 30 ps. Due to high intensity effects a remarkable slightly broadened line at 90 cm-1 appears and can be assigned to the wave packet propagation generated in the dimer's ground state by impulsive stimulated
Raman scattering. Revivals of this ground state wave packet are found at 17ps and 34ps. A comparison with other isotopes of K2 is given.
Received: 9 February 1998 / Revised: 15 May 1998 / Accepted: 2 June 1998 相似文献
12.
R. V. Turkevich D. V. Khomitsky 《Journal of Experimental and Theoretical Physics》2018,126(2):237-245
Quantum states have been calculated analytically; the dynamics of a wave packet in a magnetic field has been investigated, and the optical absorption coefficient has been calculated for surface states in 3D topological insulators of the Bi2Te3 family. We have detected a qualitative effect of the hexagonal warping of the spectrum on the structure of wavefunctions at the Landau levels, its manifestation in the features of the wave packet dynamics in a quantizing magnetic field, as well as in the frequency dependence of the optical absorption coefficient, in which new peaks that are absent in the isotropic model of the spectrum appear depending on the polarization of the incident wave. The effects considered here can be manifested in the optical and transport experiments with topological insulators, which makes it possible to determine the parameters of their band structure. 相似文献
13.
W. Chin M. Mons I. Dimicoli F. Piuzzi B. Tardivel M. Elhanine 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):347-355
By using depopulation laser techniques, like IR-UV population labeling coupled to mass-selected R2PI detection, we confirm
that four tautomers are responsible for the near UV spectroscopy (310-280 nm) of guanine: two enol and two keto forms, each
pair having a 7NH and a 9NH form. Besides the UV spectroscopy of each tautomer, additional information on the excited state
nature and dynamics is obtained from fluorescence studies. In particular, the quenching of fluorescence beyond 285 nm, the
existence of a background absorption, as well as the existence of a strongly red-shifted component in the fluorescence emission
provides evidence for a strong electronic mixing in the excited state together with an efficient non-radiative process. The
details of these features are found to be tautomer-dependent. Comparison of the present results with literature data on other
purine molecules, like adenine or 9-substituted guanines, enables us to propose a new insight on the spectroscopy and dynamics
of the purine molecules. First, a large variability of the tautomer distribution in the gas phase is found within the purine
family, in particular a molecular change, as simple as a 9-methylation on guanine, can reduce the tautomer distribution to
a single species (enol form). Since the absorption spectrum is tautomer-dependent as well as substituent-dependent, it turns
out that the tautomer population is one of the major parameters that control the overall shape of the UV spectrum. Second,
the excited state model, often evoked in the literature, which involves electronic coupling between excited states of different
natures, namely ππ* and nπ* states, might account for the present fluorescence measurements on guanine, providing an extensive excited state electronic
mixing is assumed for these systems.
Received 24 June 2002 Published online 13 September 2002 相似文献
14.
Four wave mixing (FWM) is of considerable interest in generation of a phase conjugate beam with photorefractive crystals. The common methods of FWM are parallel polarization FWM and cross polarization FWM. In this paper, we analyze the phase matching property of the latter. First, we consider the phase matching condition, and derive equations representing the angler relationship of interacting beams. Then, we consider the phase mismatching which is caused by shift of the probe beam angle from the phase matching condition, and calculate the effect of the shift of this angle on the amount of phase mismatching. We also determine and closely examine the coupling constant. 相似文献
15.
The electron spin-lattice and spin-spin phase relaxation measurements of Cu2+ ions in various crystals are reviewed and discussed. Examples of the Debye temperature determination from a wide temperature range measurements of the spin-lattice relaxation time T1 are shown. An influence of the Jahn-Teller dynamics on T1 is presented. The phase relaxation described by the phase memory time TM is affected by temperature due to the spin packet width modulation by molecular motions. The TM is anisotropic in crystals and can be different for different hyperfine lines of an EPR spectrum. 相似文献
16.
E. Hasselbrink 《Applied Physics A: Materials Science & Processing》1991,53(5):403-409
The ultraviolet photochemistry of molecules adsorbed on metallic surfaces has been studied using excimer lasers as radiation source. Dissociation with the fragments either ejected into the gas phase or retained on the surface is one prominent channel. The other is photodesorption of intact molecules. The desorbing molecules are characterized by time-of-flight mass spectroscopy and laser spectroscopy. The state of the adsorbate after irradiation is characterized by thermal desorption spectroscopy and high resolution electron energy loss spectroscopy. The methods and fundamental characteristics are exemplified using results from three studied systems: O2, H2O, and N2O4 adsorbed on Pd(111). 相似文献
17.
This paper studies the quantum dynamics of electrons in a surface
quantum well in the time domain with autocorrelation of wave packet.
The evolution of the wave packet for different manifold eigenstates with
finite and infinite lifetimes is investigated analytically. It is
found that the quantum coherence and evolution of the surface electronic
wave packet can be controlled by the laser central energy and
electric field. The results show that the finite lifetime of excited
states expedites the dephasing of the coherent electronic wave
packet significantly. The correspondence between classical and
quantum mechanics is shown explicitly in the system. 相似文献
18.
Study on wave packet dynamics of E~1Σ_g~+ state of Li_2 with femtosecond-resolved photoelectron spectra
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wave packet dynamics of the Li2 molecule are investigated
by using the time-dependent quantum wave packet method, and the
time-resolved photoelectron spectra of the Li2 molecule are
calculated. The time-resolved wave packet theory is used to
reasonably interpret the phenomena of the photoelectron spectra for
different parameters. Our calculation shows that the loss of the
wave packets in the shelf state area of E{ }^1\Sigmag^ +
plays a prominent role in the process of photoionization with the
increase of the delay time. Moreover, the oscillation of the wave
packet on the E{ }^1\Sigmag^ + curve symbolizes a
decreasing process of energy. 相似文献
19.
F. Conti C. Corvaja M. Maggini F. Piu G. Scorrano A. Toffoletti 《Applied magnetic resonance》1997,13(3-4):337-346
Fulleropyrroliddine derivatives containing a TEMPO group (FPNOs) are examined in toluene solution, between 200 and 270 K, by TR-EPR spectroscopy after LASER excitation. Signals of the ground and excited states are observed and their time profiles are recorded. In presence of ferrocene the time pattern of the polarization is modified, showing the occurrence of intermolecular electron transfer from the donor ferrocene to the excited FPNOs. The rate constantk E. is obtained from the simulation of the EPR signal time evolution of the ground and excited states. 相似文献
20.
By applying ultrafast pump-probe spectroscopy with 15 fs temporal resolution to (TMTTF(+))(2) dimers we provide a full picture of the structural relaxation following photoexcitation of their CT transition. Both population and coherent phonon dynamics allow tracking wave packet motion onto the multidimensional excited state potential energy surface, as obtained by density functional theory calculations. We show that the vibrations that are strongly coupled to the charge-transfer transition of the dimer correspond to those driving the photoinduced phase transition occurring in charge-transfer crystalline solids. 相似文献