Chromium dihydride (CrH2): theoretical evidence for a bent 5B2 ground state

Ab initio molecular electronic structure theory has been used to study two likely candidates for the quintet ground state of CrH₂ at the self-consistent field, the single and double excitation configuration interaction (CISD), the single and double excitation coupled cluster (CCSD), and the single, double, and perturbative triple excitation coupled cluster (CCSD(T)) levels of theory. The largest basis sets utilized for geometry optimizations, designated two-f TZ2P, have a contraction scheme of Cr(14s11p6d2f/10s8p3d2f), H(5s2p/3s2p). At the CCSD(T) level of theory using this two-f TZ2P basis, a bent (C_2v symmetry) ⁵B₂ state is predicted to lie a mere 4·2 kcal mol^-1 (4·5 kcal mol^-1 including zero-point vibrational energy correction) lower in energy than linear (D_∞h symmetry) ⁵Σ_g ⁺ HCrH. Theoretical predictions for the equilibrium geometry, harmonic vibrational frequencies, and isotopic frequency shifts of the ⁵B₂ state compare favourably with the results of recent matrix isolation FT-IR work by Xiao, Hauge, and Margrave. The two-f TZ2P CCSD(T) optimized geometry of ⁵B₂ CrH₂ is r _e = 1·658 Å and ?_e = 114·4° (118° ± 5° is the experimentally estimated bond angle), while the harmonic vibrational frequencies are ω₁(a₁) = 1710, ω₂(a₁) = 582, and ω₃(b₂) = 1683 cm^-1 (experimentally assigned fundamentals in an argon matrix are the symmetric stretch 1651 cm^-1 and asymmetric stretch 1615 cm^-1). Isotopic frequency shifts of CrD₂ relative to CrH₂ are Δω₁(a₁) = -492 and Δω₃(b₂) = -477 cm^-1 (compared with symmetric stretch -462 cm^-1 and asymmetric stretch -448-cm^-1 from experiment).     

洞态氩离子的退激发及末电离态离子分布的理论研究

在描述洞原子(或离子)退激发过程只考虑单俄歇跃迁和辐射跃迁的辐射-单俄歇级联退激发模型的基础上,进一步考虑了双俄歇跃迁的贡献,发展了辐射-单俄歇-双俄歇级联退激发模型.据此模型研究了Ar⁺(1s^-1)(1s洞态氩离子)和Ar⁺(2s^-1)(2s洞态氩离子)的退激发过程及末电离态离子的分布,获得了与实验相符的结果. 关键词： 辐射-单俄歇级联退激发模型 双俄歇跃迁 辐射-单俄歇-双俄歇级联退激发模型 洞离子退激发     

Frequency stabilization of a laser diode to hyperfine structure of the 4D5/2 state of Rb atoms

We observed hyperfine structures of the 4D_5/2 state of ⁸⁵Rb atoms and applied them to the frequency stabilization of a laser diode by using the double resonance optical pumping (DROP). The hyperfine structures of the 4D_5/2 states of ⁸⁵Rb atoms were highly resolved in the Rb vapor cell. We compared the DROP with the optical-optical double resonance (OODR) in the 5S_1/2-5P_3/2-4D_5/2 ladder-type system of ⁸⁵Rb atoms. When we stabilized the frequency of a laser diode to the hyperfine structure of the 5P_3/2(F″ = 4)-4D_5/2(F″ = 3) transition by using the DROP spectrum, the frequency stability was approximately 2.3 × 10^− 12 after 100 s.     

Continuously transferring cold atoms in caesium double magneto-optical trap

We have established a caesium double magneto-optical trap (MOT) system for cavity-QED experiment, and demonstrated the continuous transfer of cold caesium atoms from the vapour-cell MOT with a pressure of ～ 1×10^-6 Pa to the ultra-high-vacuum (UHV) MOT with a pressure of ～ 8×10^-8 Pa via a focused continuous-wave transfer laser beam. The effect of frequency detuning as well as the intensity of the transfer beam is systematically investigated, which makes the transverse cooling adequate before the atoms leak out of the vapour-cell MOT to reduce divergence of the cold atomic beam. The typical cold atomic flux got from vapour-cell MOT is ～2×10⁷ atoms/s. About 5×10⁶ caesium atoms are recaptured in the UHV MOT.     

H<Superscript>+</Superscript><Emphasis Type="Bold">and He</Emphasis><Superscript>2+</Superscript> impact single and double ionization of lead

H⁺ and He²⁺ impact single and double ionization cross sections of ground state lead atoms have been calculated in the binary encounter approximation. Calculations of direct double ionization cross sections have been performed in the modified double binary encounter model. The accurate expressions of σ_ΔE (cross-section for energy transfer ΔE) and Hartree-Fock velocity distributions for the target electrons have been used throughout the calculations. Contributions to double ionization from Auger effect following ionization of inner shells have been considered in the present work. Our H⁺ impact single and double ionization cross sections are in good agreement with the experimental observations. In calculations of He²⁺ impact cross sections, the present theoretical approach shows limited success in the experimentally investigated region (50–350 keV amu^-1).     

A 13C NMR study of hindered rotation in N1N1 - 3-oxapentamethylene - N2 - substitutedphenyl - formamidines

Rates of rotation about partial double CN¹ bond in nine N¹N¹ - 3-oxapentamethylene - N² - substitutedphenylformamidines were determined from line shape analysis of ¹³C NMR spectra. The hight of the barrier to rotation i.e.ΔG^≠₂₉₈ correlates with i/ Hammett's 6 of substituent at phenyl ring ii/ δ ¹³C of functional carbon and iii/ the values of pKa of the above formamidines and is in the range: 54.8 to 62.9 kJ. mol⁻¹.     

First-principles study of electronic and elastic properties of Stone–Wales defective zigzag carbon nanotubes

The interaction and coupling between the electrical, mechanical properties and formation energy for SW defective (10,0) carbon nanotube is studied in density functional theory. The investigated configurations include the axial and circumferential orientations for single defect as well as four distribution types for double ones. The more stable defective configurations, namely, SW-I configurations for single SW defective carbon nanotube and II–II-(2) and I–I ones for double SW defective tubes are related to high symmetry distribution of the defects. Moreover, we found that the σ^?–π^* hybridization induced by curvature effect causes the semiconductor to metal transition for double axial SW defects case. Young's modulus reduction of SW defective carbon nanotube with respect to defect-free one is less than 8%. The energy bands and Young's moduli of double SW defective tubes are mostly affected by the defect distribution and concentration but insensitive to the circumferential distance between the double defects.     

A selective [4 + 2]-like cycloaddition of α, β-unsaturated ketone on Si(1 1 1)-7 × 7

The interaction of ethyl vinyl ketone (EVK) with Si(1 1 1)-7 × 7 has been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. The disappearance of both stretching vibrations of CH₂ (3099 cm⁻¹) and CO (1684 cm⁻¹) coupled with the appearance of new CC stretching mode (1660 cm⁻¹) in the HREELS spectra of chemisorbed EVK clearly demonstrates the direct involvement of conjugated CC and CO bonds to form a SiC¹H₂C²HC³(C⁴H₂C⁵H₃)OSi surface species via [4 + 2]-like cycloaddition in a highly selective manner. In addition, XPS studies show that the C1s binding energies of C¹/C² and C³ upon chemisorption display chemical downshifts of 0.8 eV and 2.2 eV, respectively, further confirming the proposed [4 + 2]-like cycloaddition reaction for the EVK/Si(1 1 1)-7 × 7 system. DFT theoretical calculations suggest that the proposed [4 + 2]-like cycloadduct is thermodynamically most favorable.     

The puzzling infrared spectra of the nitric oxide dimer radical cation: a systematic application of Brueckner methods

Since symmetry breaking occurs in the ONNO⁺ cation with the self-consistent field (SCF) method and inverse symmetry breaking occurs when density functional theory (DFT) methods are used, Brueckner double excitation coupled cluster methods (BD) and BD plus perturbative triple-excitation contributions [BD(T)]have been used to study the geometries and vibrational frequencies for the trans and cis structures of the ONNO⁺ cation. Double-ζ plus polarization (DZP) basis sets and triple-ζ plus double polarization with f functions (TZ2Pf) basis sets were utilized. The ground state of the trans-ONNO cation is of ²A_g symmetry, which has a slightly (0.36 kcalmol^-1) lower energy than the cis conformer (²A₁). The controversial vibrational frequency corresponding to the asymmetric N–O stretching mode for both trans and cis structures is predicted as about 1600cm^-1. This value is discussed in the context of the many (sometimes variant) experimental assignments.     

Effective Dynamics of Double Solitons for Perturbed mKdV

We consider the perturbed mKdV equation \({\partial_t u = -\partial_x (\partial_x^2u + 2u^3- b(x,t)u)}\) , where the potential \({b(x,t)=b_0(hx,ht), 0 < h \ll 1 }\) , is slowly varying with a double soliton initial data. On a dynamically interesting time scale the solution is \({ {\mathcal{O}}(h^2) }\) close in H ² to a double soliton whose position and scale parameters follow an effective dynamics, a simple system of ordinary differential equations. These equations are formally obtained as Hamilton’s equations for the restriction of the mKdV Hamiltonian to the submanifold of solitons. The interplay between algebraic aspects of complete integrability of the unperturbed equation and the analytic ideas related to soliton stability is central in the proof.     

Photolysis and E. S. R. Studies on Triphenylphosphinecarbethoxymethylene

Although several different groups have studied the photolysis of phosphorus ylides, none have utilized e. s. r. to support the postulated decomposition mechanisms. The fundamental question which awaits a definitive answer is which bond breaks first upon photolysis. Tschesche¹ and de Silva² utilizing the ylides (1) and (2) suggested that the carbon-phosphorus double bond was initially broken while Nagao³ using (3) proposed phenyl-phosphorus bond cleavage.     

NO2分子的光学-光学双色双共振多光子离化谱

以Nd:YAG激光器的二倍频输出光为抽运光,其三倍频输出抽运的光学参量发生/放大器输出光为探测光,利用光学-光学双色双共振多光子离化光谱技术(OODR-MPI),获得了NO₂分子在605—675nm探测光波长范围内的多光子离化激发谱. 通过对NO₂分子离化机理的分析,确定了在此波长区间,NO₂分子经1+3+1双共振多光子过程离化,离化通道为NO₂(X²A₁)hν 关键词： 2')" href="#">NO₂ 光学-光学双共振多光子离化谱 里德伯态 分子常数     

Synchrotron radiation VUV double photoionization of some small molecules

The VUV double photoionizations of small molecules (NO,CO,CO2 ,CS2 ,OSC and NH3 ) were investigated with photoionization mass spectroscopy using synchrotron radiation. The double ionization energies of molecules were determined with photoionization efficiency spectroscopy. The total energies of these molecules and their parent dications (NO2+ ,CO2+ ,CO2+2 ,CS2+2 ,OSC2+ and NH2+3 ) were calculated using the Gaussian 03 program and Gaussian 2 calculations. Then,the adiabatic double ionization energies of the molecules were predicated by using high accuracy energy mode. The experimental double ionization energies of these small molecules were all in reasonable agreement with their respective calculated adiabatic double ionization energies. The mechanisms of double photoionization of these molecules were discussed based on a comparison of our experimental results with those predicted theoretically. The equilibrium geometries and harmonic vibrational frequencies of molecules and their parent dications were calculated by using the MP2 (full) method. The differences in configurations between these molecules and their parent dications were also discussed on the basis of theoretical calculations.     

Sensitivity of nuclear-quadrupole double-resonance detection of half-integer spin nuclei

The sensitivity of the Slusher and Hahn’s nuclear quadrupole double resonance technique is calculated in general for an arbitrary nuclear spin S of the quadrupole nuclei and for an arbitrary asymmetry parameter η of the electric field gradient tensor. The nuclear spin S = 5/2 (¹⁷O, ²⁵Mg, …) is treated in details. The influence of the cross-relaxation rate between the quadrupole nuclei and the abundant spin system on the sensitivity of double resonance is discussed. The results of the theoretical analysis are applied in the analysis of the ¹H–¹⁷O nuclear quadrupole double resonance spectra in p-toluenesulfonamide and 2-nitrobenzoic acid. The 17O nuclear quadrupole resonance frequencies from a sulfonamide group are determined for the first time. The proton–oxygen cross-relaxation rates and the proton local frequency in zero external magnetic field are experimentally determined from the nuclear quadrupole double resonance spectra.     

Die Hyperfeinstruktur des 32P3/2-Zustands von Natrium im starken Magnetfeld

The hyperfine structure of the 3²P_3/2 State of Na²³has been measured by the optical double resonance technique in a magnetic field of 3.1 kG sufficiently strong to decouple completelyI andJ. In the case of π or (σ⁺+σ^?) excitation the double resonance signal represents the superposition curve of eight unresolved radio-frequency transitions. The dependence of the signal on the pressure of sodium vapour and the radio-frequency field strength has been studied. The analysis of the experimental curves yields for the hyperfine coupling constants the valuesa=(18.7±0.4) Mc/s andb=(3.4±0.4) Mc/s. The nuclear electric quadrupole moment derived from the ratio ofb/a isQ=(0.146±0.02) · 10^?24cm². The Lande factor and the lifetime for the 3²P_3/2state are g_J=1.3344±0.0004 and τ=(1.61±0.07) · 10^?8 sec.     

An AlGaN/GaN HEMT with reduced surface electric field and improved breakdown voltage

A reduced surface electric field in AlGaN/GaN high electron mobility transistor (HEMT) is investigated by employing a localized Mg-doped layer under the two-dimensional electron gas (2-DEG) channel as an electric field shaping layer. The electric field strength around the gate edge is effectively relieved and the surface electric field is distributed evenly as compared with those of HEMTs with conventional source-connected field plate and double field plate structures with the same device physical dimensions. Compared with the HEMTs with conventional source-connected field plate and double field plate, the HEMT with Mg-doped layer also shows that the breakdown location shifts from the surface of the gate edge to the bulk Mg-doped layer edge. By optimizing both the length of Mg-doped layer, L_m, and the doping concentration, a 5.5 times and 3 times the reduction in the peak electric field near the drain side gate edge is observed as compared with those of the HEMTs with source-connected field plate structure and double field plate structure, respectively. In a device with V_GS=-5 V, L_m=1.5 μm, a peak Mg doping concentration of 8× 10¹⁷ cm^-3 and a drift region length of 10 μm, the breakdown voltage is observed to increase from 560 V in a conventional device without field plate structure to over 900 V without any area overhead penalty.     

新型激光晶体Yb:KY(WO4)2的结构与光谱

采用顶部籽晶提拉法，以K₂W₂O₇为助溶剂，生长了Yb:KY(WO₄)₂新型激光晶体.经热重-差热分析，确定晶体熔点为1045℃，相变温度为1010℃.X射线粉末衍射测试，验证所生长的晶体为β-Yb:KY(WO₄)₂.晶体结构分析确定Yb:KY(WO₄)₂晶体由WO₆八面体连接而成，WO₆八面体是由双氧桥(WOOW)及单氧桥(WOW)构成.晶体粉末样品室温下的红外及拉曼光谱测试，确定WO₆原子基团、双氧桥及单氧桥的振动频率.晶体的吸收峰位于940nm，980nm，发射峰位于989nm—1030nm. 关键词： 晶体结构 光谱 晶体生长     

Energy shifts and forbidden transitions in H+ 2 due to electronic g/u symmetry breaking

A full account is given of calculations and measurements of transition frequencies and intensities of the forbidden pure rotation transition (v = 19, N = 1)-(v = 19, N = 0) in the ground electronic state (1sσ_g) of H⁺ ₂. The transition has measurable intensity because of ortho-paru mixing that arises from electronic g/u symmetry breaking caused by the Fermi contact hyper-fine interaction. Measurements of the transition were made in both single and double resonance using a fast ion beam/microwave spectrometer. The transition frequency was determined to be at 14961.7 ± 1.1 MHz (95% confidence, 5 measurements), in excellent agreement with the theoretical prediction of 14960 ± 3 MHz. The intensity of the transition relative to the allowed 1sσ_g (v = 19, N = 1)-2pσ_u,(v = 0, N = 2) transition was estimated from the available measurements to be 8000, in reasonable agreement with the theoretically predicted value of ?3000.     

Zur Hyperfeinstruktur des 62P3/2-Terms von Rb87

The hyperfine structure of the 6² P _3/2 state of Rb⁸⁷ has been reinvestigated with optical double resonance in zero magnetic field. The results for the hfs-splitting constants areA(6² P _3/2, Rb⁸⁷)=27.70 (2) Mc/s andB(6² P _3/2, Rb⁸⁷)=3.94 (4) Mc/s. From these constants one obtains a value for the nuclear quadrupole moment uncorrected for shielding effects ofQ=+0.138 (1)·10^?24 cm².     

以慢原子束方式进行原子转移的双磁光阱系统

建立了一套用于玻色-爱因斯坦凝聚实验的铷原子双磁光阱装置.从低速强源中获得慢原子束，向超高真空磁光阱进行原子转移.低速强源磁光阱与超高真空磁光阱之间可维持3个量级的压强差,超高真空磁光阱的真空度最高可达1×10^-9 Pa. 慢原子束的束流通量达1×10⁹/s. 约4×10⁸个⁸⁷Rb原子被装载到超高真空磁光阱中.还讨论了两种典型情况下磁光阱中装载的最大原子数.