Calculation of vibrational energy transition rates in acoustic relaxation processes for excitable gas molecules

To research the correlation between vibrational energy transition rates and acoustic relaxation processes in excitable gases, the vibrational relaxation theory provided by Tanczos [J.Chem. Phys. 25, 439(1956)] is applied to calculate the energy transition rates of VibrationalVibrational(V-V) and Vibrational-Translational(V-T) energy transfer in gas mixtures. The results of calculation for the multi-relaxation processes in various gas mixtures, consisting of carbon dioxide, methane, chlorine, nitrogen, and oxygen at room temperature, demonstrate that the acoustic energy stagnated in every vibrational mode is coupled with each other through V-V energy exchanges. The vibrational excitation energy will relax through the V-T de-excitation path of the lowest mode because of its fastest V-T transition rate, resulting in that only one absorption peak can be measured for most of excitable gas mixtures. Thus, an effective model is provided to analyze how the vibrational energy transition rates affect the characteristics of acoustic relaxation processes and acoustic propagation in excitable gas mixtures.     

可激发气体分子声弛豫过程振动模式能量转移速率计算

研究可激发气体中振动模式能量转移速率和声弛豫过程形成的关系,将单一气体Tanczos弛豫方程理论[J.Chem.Phys.25,439(1956)]扩展应用于混合气体中振动模式的振动-振动(V-V)和振动-平动(V-T)能量转移速率的计算。在室温下CO₂,CH₄,CL₂,N₂和O₂组成的多种混合气体中,振动模式能量转移速率的计算结果表明:对于多个振动模式所形成的声复合弛豫过程,各振动模式的声激发能可由V-V能量转移相互耦合后传递给具有最快V-T转移速率的最低振动频率振动模式,再通过该振动模式的V-T转移退激发形成主弛豫过程。这种选择最快转移路径的声激发量弛豫方式,造成了大多数可激发气体中声弛豫吸收谱的实测数据只存在一个吸收峰的现象。从而提供了一个可通过计算微观振动能量转移速率分析混合气体声弛豫过程形成机理的理论模型。     

染料分子电子激发态振动失相过程的非相干光时延四波混频研究

本文对噁嗪(Oxagine)、甲酚紫(cresyl violet)染料分子的吸收带和吸收边进行了非相干光时延四波混频(TDFWM-IL)的详细研究,得到了有关失相参量的数据,并利用非相干光时延四渡混频的多能理论解释了实验结果和失相参量的物理意义。     

Collision relaxation cross section of highly vibrationally excited molecules

Through quantum-beat spectroscopy collision relaxation of a high vibrational level of SO2 at 44 877.52 cm(-1) is characterized. This is a first measurement of collision relaxation for a single, highly excited vibrational level. The deduced relaxation cross section of this excited level by Ar is 216 A(2), 5 times the area of the hard sphere, and by an ambient temperature SO2 molecule is 969 A(2), almost 20 times the hard sphere. These cross sections indicate that relaxation collisions of highly vibrationally excited molecules have effective distances much longer than van der Waals radii and involve mechanisms qualitatively different from lower excitations.     

Heterogeneous relaxation of molecule vibrational energy on metals

A mechanism of heterogeneous relaxation of a molecule vibrational energy on metal via conduction electrons is proposed. The probability of vibrational transition W of a molecule adsorbed on metal surface is calculated. The not very sharp dependence of W on the distance between the molecule and the metal surface, on metal parameters and on the molecular vibrational quantum provides a satisfactory explanation of the experimental data available.     

A role of solvent in vibrational energy relaxation of metalloporphyrins

The formation of a vibrationally excited photoproduct of metalloporphyrins upon (π, π*) excitation and its subsequent vibrational energy relaxation were monitored by picosecond time-resolved resonance Raman spectroscopy. Stokes Raman bands due to a photoproduct of nickel octaethylporphyrin (NiOEP) instantaneously appeared upon the photoexcitation. Their intensities decayed with a time constant of 300 ps, which indicates electronic relaxation from the (d, d) excited state (B_1g) to the ground state (A_1g), being consistent with the results of transient absorption measurements by Holten and coworkers. Anti-Stokes ν₄ and ν₇ bands for vibrationally excited (d, d) state of NiOEP decayed with time constants of 10 and 300 ps. The former is ascribed to vibrational relaxation, while the latter corresponds to the electronic relaxation from the (d, d) excited state to the electronic ground state. While the rise of anti-Stokes ν₄ intensity was instrument-limited, the rise of anti-Stokes ν₇ intensity was delayed by 2.6±0.5 ps, which indicates that intramolecular vibrational energy redistribution has not been completed in subpicosecond time regime. To study a mechanism of intermolecular energy transfer, solvent dependence of the time constants of anti-Stokes kinetics was investigated using various solvents. No significant solvent dependence of the rise and decay constants was observed for NiOEP. For an iron porphyrin, we observed two phases in intermolecular energy transfer. The fast phase was insensitive to solvent and the slow phase depended on solvents. A model of classical thermal diffusion qualitatively reproduced this behavior. For solute-solvent energy transfer process, low-frequency modes of proteins seem to be less important.     

Wavelength-dependent rotation of dye molecules in a polar solution

Investigation of rotation movement of 3-amino-N-methylphthalimide in glycerol was carried out, taking into consideration the fluctuation of solvate structure. It was shown theoretically and experimentally that structural relaxation of the solvate shell, which follows excitation of the dye molecule, causes not only shift of the fluorescence spectrum in time but also additional rotation of the dye molecule. This effect, which may be called wavelength-dependent rotation, depends on the light frequency of both excitation and fluorescence. In particular, at excitation near the maximum of the absorption band, when the relaxation process is followed with the red shift of the fluorescence maximum, the anisotropy of fluorescence decreases faster in the red part of the fluorescence band than in the blue part. On the contrary, in the case of far anti-Stokes excitation, when the temporal shift of fluorescence is going to the blue, the anisotropy in the red part of the spectrum drops more slowly than in the blue part. Finally, there is a special excitation frequency which causes neither change of the fluorescence maximum nor acceleration of the rotational movement of the dye molecule. It is also shown that the temporal evolution of the spectrum and anisotropy of fluorescence in a polar dye solution may be quantitatively described using the socalled inhomogeneous broadening function (IBF). This function gives the distribution of dye molecules in a solution over frequencies of pure electronic transition due to fluctuations of the surrounding shell structure. Measurements of IBF changes in time carried out for 3-amino-N-methylphthalimide showed that during first 3 ns after excitation, the half-width of the IBF grows, and at the same time its maximum quickly shifts to the red. At the later time period there are only small changes of IBF position but considerable exponential decrease in its half-width. The IBF during this period preserves the Gaussian shape.     

Numerical calculations of emission probabilities of primarily excited molecules in dye solutions

The “active sphere” concentration depolarization theory of Jabloński involves the probability, W_Dk, that a photon is emitted by the donor. Up till now, the mean value of W_Dk, has been exactly calculated only for k = 2 (1 donor and 1 acceptor in the active sphere). For k > 2 the approximate method of Knox was employed. In this paper the use of the Monte Carlo integration method to find <W_Dk > for k up to ten is described. The more accurate values thus obtained coincide closely with the ones found using the simplified method. This finding validates the use of the latter method without reservation up to high dye concentration.     

Bimolecular quenching of fluorescence and interaction between excited molecules in solution

Bimolecular quenching of fluorescence was observed for fluoranthene, coronene and 3,4-benzophenanthrene in 1,2,4-trichlorobenzene or tetrahydrofuran solution, and the rate constant of the process was determined at various temperatures between room temperature (295 K) and 77 K. The bimolecular quenching rate constant was found to be a little smaller than that for a diffusion-controlled process in a fluid solvent. From the temperature dependence of the rate constant the quenching was found to be due to the long-range interaction which is enhanced by diffusion of the excited molecules in fluid media.     

卟啉酞菁二元分子光谱及激发态弛豫的非简并四波混频研究

通过对卟啉酞菁二元分子TTPP-O-Pc和TTPP-O(CH_2)_5-O-Pc的发射光谱和激发光谱的系统研究,证实了(tetratolylphenyl porphyrin)TTPP到Pc的能量转移,区分了后一种材料中发射光谱的两组谱带的来源.利用非简并四波混频(NDFWM)方法研究了二元分子激发态弛豫过程,获得了这两种材料的激发态弛豫时间分别为3.6ps和4ps,以及电荷弛豫时间分别为18.5ps和82ps.     

Simultaneous measurements of absorption and vibrational relaxation time in CF2HCl molecules

Summary We describe in this paper a simple interferometric technique which allows a direct and simultaneous determination of energy absorption and of the vibrational-translational relaxation time of polyatomic molecules strongly excited by reasonant, infrared (10.6 μm) laser radiation. In particular, we have applied this method to the study of freon-22 (CF₂HCl), a medium-size molecule that, apart from its potential application in¹³C isotope separation, shows interesting absorption features in the 10 μm region. The results are also compared with our previous findings in SF₆. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Vibrational relaxation of dye molecules investigated by ultrafast induced dichroism

Theoretical and experimental data are presented on the propagation of picosecond pulses in weakly excited dye solutions. It is shown that the so called coherence peak of the induced dichroism observed at short delay times depends on the vibronic relaxation and the excited state absorption of the dye molecules. Interpretation of the experimental results is considerably facilitated at low excitation level. The vibrational relaxation time in theS ₁ state of phenoxazone 9 was measured to be _v =0.8±0.3 ps, 0.7±0.2 ps and 0.7±0.2 ps, respectively, for the solvents dioxane, solid polystyrene and CCl₄. For rhodamine 6 G in ethanol we find _v =0.5±0.2 ps.     

Slow energy relaxation of macromolecules and nanoclusters in solution

Many systems in the realm of nanophysics from both the living and the inorganic world display slow relaxation kinetics of energy fluctuations. In this Letter we propose a general explanation for such a phenomenon, based on the effects of interactions with the solvent. Within a simple harmonic model of the system fluctuations, we demonstrate that the inhomogeneity of coupling to the solvent of the bulk and surface atoms suffices to generate a complex spectrum of decay rates. We show for myoglobin and for a metal nanocluster that the result is a complex, nonexponential relaxation dynamics.     

LiAl分子基态、激发态势能曲线和振动能级

利用单双激发多参考组态相互作用方法获得了LiAl分子基态X¹∑⁺及七个激发态a³∏, A¹∏, b³∑⁺, c³∑⁺, B¹∏, C¹∑⁺, d³∏的势能曲线, 通过势能曲线得到各态的平衡核间距R_e, 进而求得绝热激发能和垂直激发能.计算结果表明:c³∑⁺ 电子态是一个不稳定的排斥态, A¹∏态是一个较弱的束缚态, 其余6个电子态均为束缚态; b³∑⁺与 c³∑⁺态之间存在预解离现象; 8个电子态分别解离到两个通道, 即Li(²S)+Al(²P⁰)与Li(²P⁰)+Al(²P⁰). 接着将势能曲线拟合到Murrel-Sorbie解析势能函数形式, 据此获得各态的光谱数据:基态X¹∑⁺的平衡键长为0.2863 nm, 谐振频率为316 cm^-1, 解离能D_e为1.03 eV, 激发态a³∏, A¹∏, b³∑⁺, c³∑⁺, B¹∏, C¹∑⁺, d³∏的垂直激发能依次为0.27, 0.83, 1.18, 1.14, 1.62, 1.81, 2.00 eV; 解离能依次为1.03, 0.82, 0.26, 排斥态, 1.54, 1.10, 0.93 eV, 相应谐振频率 ω_e为339, 237, 394, 排斥态, 429, 192, 178 cm^-1. 通过求解核运动的薛定谔方程找到了J=0时 LiAl分子7个束缚电子态的振动能级和转动惯量. 关键词： LiAl 光谱常数 势能曲线 振动能级