Cumulant functions in optical coherence theory

Cumulant functions are introduced to describe the statistical state of a radiation field. These functions are simply related to the optical coherence functions but have some interesting features. It is shown that if the cumulant functions of all orders greater than some numberN ₀ vanish then they also vanish for all orders greater than 2. Thermal field is the only field having this property. This property holds whether the field is described by a classical stochastic process or by a quantum density operator. Further the particular operator ordering used in defining these cumulant functions for the quantized field affects only the second order cumulant function. To describe the statistical state of a vector field such as partially polarized or unpolarized radiation, one would need to introduce cumulant tensors.     

Gas phase activation energy for unimolecular dissociation of biomolecular ions determined by focused RAdiation for gaseous multiphoton ENergy transfer (FRAGMENT)

We present a novel approach for the determination of activation energy for the unimolecular dissociation of a large (>50 atoms) ion, based on measurement of the unimolecular dissociation rate constant as a function of continuous-wave CO(2) laser intensity. Following a short ( approximately 1 s) induction period, CO(2) laser irradiation produces an essentially blackbody internal energy distribution, whose 'temperature' varies inversely with laser intensity. The only currently available method for measuring such activation energies is blackbody infrared radiative dissociation (BIRD). Compared with BIRD, FRAGMENT: (a) eliminates the need to heat the surrounding ion trap and vacuum chamber to each of several temperatures (each requiring hours for temperature equilibration); (b) offers a three-fold wider range of effective blackbody temperature; and (c) extends the range of applications to include initially cold ions (e.g., gas-phase H/D exchange). Our FRAGMENT-determined activation energy for dissociation of protonated bradykinin, 1.2 +/- 0.1 eV, agrees within experimental error to the value, 1.3 +/- 0.1 eV, previously reported by Williams et al. from BIRD experiments. Copyright 1999 John Wiley & Sons, Ltd.     

铌酸锶钡薄膜的微结构与电光性能的研究

本文叙述了使用溶胶凝胶法在MgO(0 0 1)的衬底上制备铌酸锶钡薄膜的过程 ,膜层厚度可达 5 μm。通过X射线衍射、摇摆曲线、扫描、拉曼散射光谱等方法研究了薄膜的微结构性能 ,实验发现 ,铌酸锶钡薄膜具有了较好的 (0 0 1)方向的优先取向性能 ,并且随着薄膜厚度的增加 ,其晶体取向性也会随之不断改进。熔石英的透明衬底上生长的SBN薄膜具有较大的电致双折射效应 ,其有效电光系数能够高达 6 6 2× 10 -11m/V。     

M-M bond-stretching energy landscapes for M2(dimen)4(2+) (M = Rh, Ir; dimen = 1,8-diisocyanomenthane) complexes

Isomers of Ir(2)(dimen)(4)(2+) (dimen = 1,8-diisocyanomenthane) exhibit different Ir-Ir bond distances in a 2:1 MTHF/EtCN solution (MTHF = 2-methyltetrahydrofuran). Variable-temperature absorption data suggest that the isomer with the shorter Ir-Ir distance is favored at room temperature [K = ～8; ΔH° = -0.8 kcal/mol; ΔS° = 1.44 cal mol(-1) K(-1)]. We report calculations that shed light on M(2)(dimen)(4)(2+) (M = Rh, Ir) structural differences: (1) metal-metal interaction favors short distances; (2) ligand deformational-strain energy favors long distances; (3) out-of-plane (A(2u)) distortion promotes twisting of the ligand backbone at short metal-metal separations. Calculated potential-energy surfaces reveal a double minimum for Ir(2)(dimen)(4)(2+) (～4.1 ? Ir-Ir with 0° twist angle and ～3.6 ? Ir-Ir with ±12° twist angle) but not for the rhodium analogue (～4.5 ? Rh-Rh with no twisting). Because both the ligand strain and A(2u) distortional energy are virtually identical for the two complexes, the strength of the metal-metal interaction is the determining factor. On the basis of the magnitude of this interaction, we obtain the following results: (1) a single-minimum (along the Ir-Ir coordinate), harmonic potential-energy surface for the triplet electronic excited state of Ir(2)(dimen)(4)(2+) (R(e,Ir-Ir) = 2.87 ?; F(Ir-Ir) = 0.99 mdyn ?(-1)); (2) a single-minimum, anharmonic surface for the ground state of Rh(2)(dimen)(4)(2+) (R(e,Rh-Rh) = 3.23 ?; F(Rh-Rh) = 0.09 mdyn ?(-1)); (3) a double-minimum (along the Ir-Ir coordinate) surface for the ground state of Ir(2)(dimen)(4)(2+) (R(e,Ir-Ir) = 3.23 ?; F(Ir-Ir) = 0.16 mdyn ?(-1)).