玻璃中Nd3+离子4F3/2态的多声子弛豫及电子-声子相互作用

本文通过在不同温度下测定Nd³⁺离子⁴F_3/2态的荧光和寿命的方法,确定了Nd³⁺离子⁴F_3/2态的多声子弛豫率对温度的关系,并根据多声子理论和红外振动谱对过程进行了理论拟合,研究了五种玻璃⁴F_3/2态的多声子过程,确定了过程所涉及的声子能量和声子数目,分析了多声子弛豫率与基质性质的关系,进一步在钕玻璃中检验了多声子理论。     

正庚烷热裂解的反应分子动力学模拟

研究表明正庚烷热裂解的主产物是C₂H₄, H₂, CH₄以及C₃H₆,模拟结果和实验吻合很好. 温度对产物分布具有明显的影响,当温度上升,目标产物乙烯的量会迅速增加. 正庚烷转化率以及主产物的摩尔分数分别通过反应分子动力学和化学动力学模拟计算得到,两种方法模拟结果相吻合. 我们还通过动力学分析研究了正庚烷热裂解反应的动力学参数,反应活化能为47.32 kcal/mol,指前因子为1.78×10¹⁴ s^-1.     

混合气体声复合弛豫频谱的解析模型

为研究声传播和分子多模式振动能量弛豫的相互关系,本文提出了一种混合气体声 复合弛豫频谱的解析模型.该模型从振动模式微观能量转移及其耦合形成宏观弛豫过程两个角度, 分析了依赖于声频率的混合气体有效热容.并通过求解振动模式能量转移的通用弛豫方程, 最终得到可同时体现主副弛豫过程的声弛豫吸收和声频散的解析结果.仿真结果表明, 对于CO₂, CH₄, N₂和O₂组成的多种混合气体, 该模型的声吸收谱与实验数据相符,峰值误差在1%以内,且反映了多振动模式形成的 声复合弛豫吸收谱上通常仅会显现1-2个吸收波峰的物理现象.与已有模型相比, 本解析模型可直接求出混合气体声弛豫频谱上特征点的解析形式,并利于对其进行定性定量分析. 从而为研究声传播特性与气体分子弛豫特性的相互关系提供了一个有效理论模型.     

异戊二烯解离光电离理论研究

利用CBS-QB3理论计算方法研究了异戊二烯的可能解离通道.获得了主要碎片离子C₅H₇⁺,C₅H₅⁺,C₄H₅⁺,C₃H₆⁺,C₃H₅⁺,C₃H₄⁺,C₃H₃⁺的C₂H₃⁺的结构以及这些解离通道的解离能,并给出了相应的过渡态和中间体的结构和位垒.得到的异戊二烯电离势及主要碎片离子的出现势均与实验值符合的较好.最后,通过理论和实验结果的对比讨论了各通道的解离机理.     

环戊酮光电离解离的实验和理论研究

本文介绍了真空紫外光电离质谱结合理论计算研究环戊酮单分子的光电离解离过程. 在9.0∽15.5 eV能量范围内,测量了环戊酮离子及其碎片离子的光电离效率曲线. 通过光电离效率曲线,将环戊酮分子的电离能确定为9.23±0.03 eV,并确认碎片离子为：C₅H₇O⁺,C₄H₅O⁺,C₄H₈⁺,C₃H₃O⁺,C₄H₆⁺,C₂H₄O⁺,C₃H₆⁺,C₃H₅⁺,C₃H₄⁺,C₃H₃⁺,C₂H₅⁺, C₂H₄⁺. 利用量子化学计算方法,在ωB97X-D/6-31+G(d,p)理论水平基础上,提出了C₅H₈O⁺的解离机制. 通过对环戊酮解离路径的分析,发现开环和氢迁移过程为环戊酮离子解离的主要路径.     

化学反应媒质中的声吸收理论及关于MgSO4水溶液的弛豫机构

本文首先应用化学热力学方法推导出弛豫吸收公式和唯象理论的假定;其次借助于Debye-Hückel离子云理论,将所得结果应用MgSO₄水溶液中去,并对以往发表的有关工作进行了讨论;最终指出,MgSO₄水溶液的弛豫吸收机构用MgSO₄←→Mg⁺⁺+SO₄^--型的反应来说明是不够恰当的。     

多量子阱结构中热载流子弛豫过程中的非平衡声子效应

在多量子阱结构中的热载流子弛豫过程中考虑非平衡声子的存在,在求解载流子能量损失率方程中同时计入声子的发射和吸收,并联立解出非平衡声子的波耳兹曼方程,从而证明,在稳态和准平衡态条件下,由载流子能量损失率方程解出的弛豫时间τ_avg,实际上是电子-声子散射时间常数与非平衡声子寿命之和,而不是以往所认为的仅为电子-声子散射时间常数。     

甲基环己烷在9∽15.5 eV能量区的真空紫外光电离研究

利用具有同步辐射源的反射式飞行时间质谱仪，研究甲基环己烷的真空紫外光电离和光解离. 观测到母体离子C₇H₁₄⁺和碎片离子C₇H₁₃⁺，C₆H₁₁⁺，C₆H₁₀⁺，C₅H₁₀⁺，C₅H₉⁺，C₄H₈⁺，C₄H₇⁺和C₃H₅⁺的光电离效率曲线. 测定甲基环己烷的电离能为9.80±0.03 eV，通过光电离效率曲线确定其碎片离子的出现势. 在B3LYP/6-31G(d)水平上对过渡态、中间体和产物离子的优化结构进行表征，并使用G3B3方法计算其能量. 提出主要碎片离子的形成通道. 分子内氢迁移和碳开环是甲基环己烷裂解途径中最重要的过程.     

平面应力对氧化亚铜晶体四个激子线系的影响

于85℃烧焊在普通玻璃上的氧化亚铜晶体样品,在77°K时受到每平方毫米10多公斤的平面压缩应力。我们系统地研究了平面应力分别垂直晶体C₄,C₃和C₂对称轴的若干样品的青和蓝激子线系的强反射线的分裂与强度。如果用Γpoee等人的假定,认为这些线系是与Γ₇⁺-Γ₈^-和Γ₈⁺-Γ₈^-带边跃迁相关,则现有的实验事实可以满意地加以解释。同样应力对这种晶体的黄和绿类氢激子线系的影响也作了研究,关于平面应力各垂直C₄,C₃和C₂对称轴的诸情形,这些系中各线的位移已被测定,其结果指示绿系的里德伯常数和线系极限受平面应力的影响比黄系的大得多。     

SBS新介质C4Cl6参数确定及性能研究

 从介质对光的吸收机理出发，研究了吸收系数较小的受激布里渊散射（SBS）新介质六氯-1,3-丁二烯（C4Cl6）。通过基本的物理参数，确定了入射光波长为1 064 nm时C₄Cl₆的SBS参数，其吸收系数约为0.003 cm^-1，声子寿命约为0.25 ns，增益系数约为4.9 cm·GW^-1。分析了入射光波长与介质SBS参数的关系，布里渊频移与入射光波长成反比，声子寿命与入射光波长的平方成正比，增益系数一般与入射光波长无关。在单池SBS系统中，利用Nd:YAG调Q激光器研究了C₄Cl₆的SBS性能。实验结果表明：由于其吸收系数小，与具有相同增益系数的H₂O比较，C₄Cl₆具有较高的能量反射率（饱和能量反射率大于55%）和较宽的SBS脉宽；由于其声子寿命短，与具有相同吸收系数的CS₂比较，C₄Cl₆的SBS波形上升时间较短。吸收系数小和声子寿命短的特点，使C₄Cl₆适合作为放大池介质，这对优化SBS介质选取，提高SBS系统性能具有一定意义。     

Grüneisen parameter for HCP iron at extreme compression

The Thomas–Fermi approximation gives the Grüneisen parameter γ=γ_∞=1/2 for all materials at extreme compression (P→∞ or V→0). After re-analyzing the existing experimental data of volume dependence of Grüneisen parameter γ of hexagonal close-packed (HCP) iron, we find that γ=1/2+a(V/V ₀)^1/3+b(V/V ₀) ⁿ , where a, b and n are constants. Based on this new form of γ, the second Grüneisen parameter q, the Debye temperature θ_D and the shear sound velocity v _s of HCP iron are discussed in the present work. It is found that the zero pressure second Grüneisen parameter q ₀=0.654, which is consistent with the previously determined value of HCP iron for Earth's core physics from Dubrovinsky et al. The calculations for the Debye temperature and the shear sound velocity are also found to be in good agreement with the experimental data.     

Densities, speeds of sound and viscosities of binary liquid mixtures of octan-2-ol with benzene and halobenzenes at 298.15 and 303.15 K

Densities ρ, speeds of sound u, viscosities η and refractive indices n_D of binary mixtures of octan-2-ol with benzene, chlorobenzene and bromobenzene have been measured over the entire range of composition at 298.15 and 303.15 K and atmospheric pressure. From the experimental data, excess molar volumes V^E, isentropic compressibilities κ_S, excess isentropic compressibilities κ_S^E, and deviations of speeds of sound u^D, have been calculated at 298.15 and 303.15 K. These excess functions have been fitted to the Redlich-Kister polynomial equation. The viscosity data have been correlated using Kendall-Monroe, Grunberg-Nissan, Tamura-Kurata, Hind-Mclaughlin Ubbelohde and Katti-Chaudhary viscosity models, and McAllister's three-body interaction model at different temperatures.     

Large deviations and Lifshitz singularity of the integrated density of states of random Hamiltonians

We consider the integrated density of states (IDS) ρ_∞(λ) of random Hamiltonian H_ω=?Δ+V_ω, V_ω being a random field on ? ^d which satisfies a mixing condition. We prove that the probability of large fluctuations of the finite volume IDS |Λ|^?1ρ(λ, H_Λ(ω)), Λ ? ? ^d , around the thermodynamic limit ρ_∞(λ) is bounded from above by exp {?k|Λ|},k>0. In this case ρ_∞(λ) can be recovered from a variational principle. Furthermore we show the existence of a Lifshitztype of singularity of ρ_∞(λ) as λ → 0⁺ in the case where V_ω is non-negative. More precisely we prove the following bound: ρ_∞(λ)≦exp(?kλ^?d/2) as λ → 0⁺ k>0. This last result is then discussed in some examples.     

A thermodynamic theory of mechanical relaxation due to energy transfer between strain-sensitive and strain-insensitive modes in polymers

A thermodynamic theory has been developed on the relaxation strength of mechanical relaxation due to energy-transfer between strain-sensitive (intermolecular) modes and strain-insensitive (intramolecular) modes. Assuming that the strain-insensitive modes exhibit an overwhelmingly large heat capacity and function as a heat reservoir of constant temperature during the relaxation process, the relaxation strength ΔG, the difference between instantaneous and equilibrium moduli, is given as ΔG = TG² _Tα² ₁/C_z1, where T is the absolute temperature, G_T is the isothermal elastic modulus, and ₁ and C_z1 are the thermal expansion coefficient and the specific heat at constant strain of the strainsensitive modes, respectively. This assumption is reasonable for a polymeric solid in which backbone chains have a lot of vibrational degrees of freedom whose energy is rather insensitive to intermolecular distance and, on the contrary, the potential for localized motion such as motion of side chains is highly sensitive to intermolecular distance.

In a special case where the strain-sensitive modes are a set of vibrators with an angular frequency ω, ΔG = γ²C_z1T, where γ is the Grüneisen constant, defined by the strain-derivative of ω, = ?? In ω?z. The case where the strainsensitive modes are a set of rotators in an n-fold symmetrical potential can be treated as an extension of the above case. In the case where the strain-sensitive modes involve the transition between two states, ΔG in the present theory is reduced to that of the well-known two-state transition theory. Agreement is obtained between theory and experiment for a-methyl relaxation of poly(methy1 methacrylate).     

Sound waves in a nonequilibrium molecular gas

We consider relaxation processes of dynamics of a nonequilibrium vibrationally excited gas (T_v>T₀). It is shown that the effective heat capacities can become negative in such a medium. This leads to anomalous effects during propagation of long-wave sound: there exist regions (in the parameter T_v/T₀) of sharp enhancement and reduction of its speed, as well as regions where low-frequency sound can generally not propagate. Instability conditions are investigated for various temperature dependences of vibrational relaxation times. It is shown that in a certain region of T_v/T₀ values one has amplification of sound waves, related to the formation of second viscosity in these media. In this case a change in the amount of medium nonequilibrium can vary the sound frequency corresponding to maximum amplification.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 53–58, July, 1986.     

Excess molar volumes and isentropic compressibilities of binary liquid mixtures containing n-alkanes at 298.15 K

Excess molar volumes (V ^E) and deviation in isentropic compressibilities (Δβ _s) have been investigated from the density ρ and speed of sound u measurements of six binary liquid mixtures containing n-alkanes over the entire range of composition at 298.15 K. Excess molar volume exhibits inversion in sign in one binary mixture, i.e., n-heptane + n-hexane. Remaining five binary mixtures, n-heptane + toluene, cyclohexane + n-heptane, cyclohexane + n-hexane, toluene + n-hexane and n-decane + n-hexane show negative excess molar volumes over the whole composition range. However, the large negative values of excess molar volume becomes domainant in toluene + n-hexane mixture. Deviation in isentropic compressibility is negative over the whole range of composition in the case of all the six binary mixtures. Existence of specific intermolecular interactions in the mixtures has been analyzed in terms of excess molar volume and deviation in isentropic compressibility.     

BCl3振动激发弛豫的红外吸收研究

本工作用红外双共振技术测量了BCl₃分子的振动激发态吸收光谱。观察了分子间的多种弛豫过程及能量转移过程。得到关系式Pτ_V-V^(11BCl₃)=3微秒·托。观察到径向声波对双共振信号的调制,声速为2×10⁴厘米/秒,与计算值相符。 关键词：     

Binary hard-sphere solute-solvent radial distribution function in the colloidal limit: exact calculation from an equation of state

An exact formula is derived relating the contact value of the solute-solvent radial distribution function for an additive binary hard-sphere (HS) mixture at infinite dilution, g ^∞ ₁₂(d ₁₂), to the mixture equation of state (EOS) (1 denotes the solvent and 2 denotes the solute). This result can also be considered to be a consistency condition involving approximations for g ^∞ ₁₂(d ₁₂) and for the mixture EOS. Employing three approximate HS mixture equations of state from the literature, we use our formula to derive corresponding analytical approximations for g ^∞ ₁₂(d ₁₂) In addition, new computer simulations were performed to obtain accurate results for g ^∞ ₁₂(d ₁₂) and for g ^∞ ₁₂(r ₁₂) at the solute-solvent diameter ratios {1, 3, 5, 7, 10, 20} and the reduced solvent density ρ? = 0.8. We compare our results for g ^∞ ₁₂(d ₁₂) with the simulation results and with the results of approximate analytical expressions for g ^∞ ₁₂(d ₁₂) proposed by several workers. The results obtained from our formula in conjunction with two of the EOS expressions considered are more accurate than all previously proposed approximations, with the exception of the approximation of Matyushov and Ladanyi [1997, J. chem. Phys., 107, 5815], which is of comparable accuracy.     

Magnetic characterization of maghemite nanoparticles dispersed in surface-treated polymeric template

Magnetic characterization of maghemite nanoparticles dispersed in a polymeric template and treated under different chemical processes is reported in this work. Particle size estimated from magnetic measurements, D _M?≈?10 nm, for the free-surfactant sample, is consistent with values determined from XRD analysis and TEM images. The magnetic collapse of sextets towards a quadrupole doublet as the temperature is increased reveals the thermal relaxation of smaller $\upgamma $ -Fe₂O₃ nanoparticles. Magnetic measurements show a strong irreversibility between ZFC and FC curves suggesting the occurrence of particle–particle interaction.