钾蒸汽中双光子激发产生2^3Пg—a^3Σ^＋u扩散带受激辐射

本文报道了在Ｋ２－Ｋ中通过双光子共振激发原子或双光子激发分子产生２＾３Пｇ－ａ＾３Σ＾＋ｕ扩散带辐射的实验结果，并对激发机制以及扩散带辐射随激发能量和温度的变化进行了讨论。     

锂分子2~3π_g-a~3∑_u~+受激扩散带辐射线型的理论计算

本文利用由RKR方法计算得到的锂分子2~3∏_g态和a~3∑_u~+态(束缚部分)的势能曲线求解振动薛定谔方程,获得了2~3∏_9—a~3∑_u~+跃迁的F-C因子,自发辐射系数,进而计算了该跃迁的荧光强度和受激辐射带强度的光谱分布,其结果与实验测得的由双光子激发锂分子产生的受激扩散带辐射相吻合.     

钠分子2~3∏_g←X~1∑_g~＋双光子跃迁的研究

通过比较园偏振和线偏振两种激发方式下，钠分子的等频双光子跃迁谱线的强度变化和２３Ⅱｇ→α３∑＋ｕ辐射谱的数值拟合计算，对２３Ⅱｇ←Ｘ１∑＋ｇ的双光子跃迁进行了标识．     

钾双原子分子23ΠG-x3∑+u跃迁扩散带增益特性研究

报道了用单光子激发产生Ｋ2 23Πｇ-ｘ3∑+ｕ跃迁扩散带的实验结果，讨论了此扩散带发射增益特性随温度和缓冲气体压力等条件的变化规律。实验测得了1.2％ cm-1的增益系数。     

钠分子高位2~1Ⅱ_g与C~1Ⅱ_u态之间的碰撞能量转移

通过双光子激发和探测后向受激辐射光谱的方法观察了钠分子高位单态2~1Π_g与C~1Π-x间的碰撞能量转移过程。理论上计算的C~1Π_x态的布居分布和由C~1Π_x→X~1∑_g~+跃迁产生的紫外受激辐射光谱,均与实验结果相符。还同时采用二台不同波长的染料激光器分别激发钠分子和钠原子,研究了不同激发态钠原子对钠分子高位激发态能量转移过程的影响。     

Gd3+→Tb3+的双光子敏化发光现象

本文首次报导了Tb0.7Gd0.3P5O14非晶在DCM染料激光的激发下,Gd3+→Tb3+的双光子敏化发光现象.在考虑了Judd-Pooler的自旋轨道相互作用三级微扰项之后,较好地解释了实验结果与Axe的二级双光子吸收理论的偏差.     

激波管壁AlO自由基B~2Σ~+-X~2Σ~+和C~2Π_r-X~2Σ~+带系辐射光谱的研究

爆轰驱动过程中产生的高温高压气流对铝质膜片、激波管壁产生烧蚀和冲刷作用,以致激波管壁、端盖上附有氧化铝等杂质,而高温下AlO自由基在气体分子的高速碰撞下被激发并产生强烈的辐射,从而干扰了高温气体辐射光谱的分析。用爆轰驱动加热技术将空气加热到4 000~7 000 K,利用多通道光学分析仪对AlO自由基辐射光谱进行分析,实验发现在460~530 nm波长范围内有多支辐射非常强烈的AlO自由基B2Σ+-X2Σ+(T00=20 689 cm-1)带系辐射谱带,且每支谱带都由多个带头组成,带头间隔约为2 nm,带头处于高频位置并向低频方向伸延。通过实验与理论计算相结合,重点分析了AlO自由基B2Σ+-X2Σ+带系辐射光谱的结构特征。AlO自由基C2Πr-X2Σ+(T00=33 047 cm-1)带系辐射光谱处于270~335 nm波长范围内,其辐射强度相对于B2Σ+-X2Σ+带系较弱,并且与OH基A2Σ+-X2Π(T00=32 682 cm-1)带系辐射光谱互相干扰而难以分辨,对该波段高温空气的辐射光谱分析产生不利的影响。     

CO(A~1∏←X~1∑~+和e~3∑~-←X~1∑~+)双光子共振电离光谱的归属和双光子吸收截面的测量

我们得到了CO经过共振态A~1∏态和e~3∑~-态的转动分辨的紫外双光子共振四光子电离光谱,并测量了它们的双光子吸收截面,σ_(Xe)~(2)、σ_(A1)~(2)=1.4×10~(99)cm~8sec~(-1),σ_(A1)~(2)=2.6×10-~(50)cm~4see_(-1).用双色共振增强的方法明确地归属了受到扰动的CO A←X双光子吸收(0.0)带.     

激波管壁AlO自由基B~2∑~+-X~2∑~+和C~2∏_r-X~2∑~+带系辐射光谱的研究

爆轰驱动过程中产生的高温高压气流对铝质膜片、激波管壁产生烧蚀和冲刷作用,以致激波管壁、端盖上附有氧化铝等杂质,而高温下AlO自由基在气体分子的高速碰撞下被激发并产生强烈的辐射,从而干扰了高温气体辐射光谱的分析.用爆轰驱动加热技术将空气加热到4 000～7 000 K,利用多通道光学分析仪对AlO自由基辐射光谱进行分析,实验发现在460～530 nm波长范围内有多支辐射非常强烈的AlO自由基B~2∑~+-X~2∑~+(T_(00)=20 689 cm~(-1))带系辐射谱带,且每支谱带都由多个带头组成,带头间隔约为2 mn,带头处于高频位置并向低频方向伸延.通过实验与理论计算相结合,重点分析了AlO自由基B~2∑~+-X~2∑~+带系辐射光谱的结构特征.AlO自由基C~2∏_r-X~2∑~+(T_(00)=33 047 cm~(-1))带系辐射光谱处于270～335 nm波长范围内,其辐射强度相对于B~2∑~+-X~2∑~+带系较弱,并且与OH基A~2∑~+-X~2∏(T_(00)=32 682 cm~(-1))带系辐射光谱互相干扰而难以分辨,对该波段高温空气的辐射光谱分析产生不利的影响.     

CS_2~+经由~2Σ_u~+←~2Π_(g,3/2)跃迁的[1+1]光倒空和光碎片激发谱(英文)

用483.2nm的电离激光使CS2分子经由[3+1]REMPI制备出CS2+(X~2Πg,3/2)后,在270~285nm扫描解离激光获得了CS2+经由~B2Σu+←X~2Πg,3/2跃迁的光倒空和光碎片激发谱,由此给出了CS2+~B2Σu+电子态的振动频率ν1=613cm-1和2ν2=707cm-1.分析表明,正是CS2+的[1+1]双光子光激发解离过程导致了母体离子CS2+的光倒空和光解离成碎片离子CS+和S+,该过程中光碎片离子的分支比CS+/S+大约为3.     

Measurement and kinetics of elemental and atomic potassium release from a burning biomass pellet

Combining polarizing-filtered planar laser-induced fluorescence (PLIF) with simultaneous laser absorption, quantitative laser-induced breakdown spectroscopy (LIBS) and two-color pyrometry, the potassium release during the combustion of biomass fuels (corn straw and poplar) has been investigated. The temporal release profiles of volatile atomic potassium and potassium compounds from a corn straw show a single peak. The woody biomass, poplar, produces a dual-maxima distribution for potassium and potassium compounds. For both biomass samples, the highest concentrations of released atomic potassium and potassium compounds occur in the devolatilization stage. The mass ratios between volatile atomic potassium and potassium compounds in the corn straw and poplar cases are 0.77% and 0.79%, respectively. These values agree well with chemical equilibrium predictions that 0.68% of total potassium will be in atomic form. A two-step kinetic model of potassium release has been developed, which gives better predictions during the devolatilization stage than the existing single-step model. Finally, a map of potassium transformation processes during combustion is developed. Starting with inorganic and organic potassium, there are eight proposed transformation pathways including five proposed release pathways that occur during the combustion. The pathways describe the transformation of potassium between the fuel volatile matter, char, and ash. Potassium release during the devolatilization stage is due to pyrolysis and evaporation; during the char burnout stage, potassium release is due to char oxidation and decomposition; and during the ash cooking stage, potassium release is caused by reactions between the ash and H₂O in the co-flow.     

SIMS investigation of the Si(111) oxidation promoted by potassium overlayers

The removal of the potassium is a critical issue in the Si oxidation promoted by potassium overlayers. The effects of the morphology of the potassium and SiO₂ overlayers on the potassium desorption process have been investigated using a very sensitive technique: SIMS. For a uniform potassium overlayer (monolayer, simultaneous oxygen/potassium adsorption or multilayers exposed to low O₂ pressure) there is no evidence of a significant amount of potassium left after its desorption. However, under specific conditions: potassium multilayers exposed to high O₂ pressure (in which SiO₂ islands were observed using SEM), there is a significant amount of potassium left under the surface after the desorption attempt. These effects of the overlayer morphologies allow us to explain some reported contradictory results.     

Thermostimulated surface segregation processes in ionic crystals: Potassium chloride

The chemical and phase composition, and cleavage surface morphology and the vapor composition of potassium chloride (KCl) crystals formed as a result of the thermostimulated surface autosegregation (TSAS) are studied by methods of microprobe analysis, high-resolution scanning electron microscopy, optical digital microscopy, and quadrupole mass spectrometry. It is experimentally found that the stoichiometry (K/Cl <1) in the surface layers changes due to a decrease in the potassium surface concentration from 5% in the initial samples to 12% after annealing at a temperature of 1023 K. After annealing at a temperature of 573 K for 5 h at P = 10^?3 Pa, the potassium deficiency increases to 17%. The competing processes resulting in TSAS in potassium chloride are the self-diffusion of potassium to the surface and its subsequent sublimation. During the annealing processes the sublimation of potassium dominates, but at a temperature near fusion, the self-diffusion of potassium to the surface increases. It is concluded that potassium chloride analogous to sodium chloride is a rather stable compound to TSAS. This is an additional argument of the important role of ionic bonds in a decrease in the tendency of chemical compounds to surface autosegregation.     

钾扩散耦合引起的心脏中螺旋波的变化

在某些情况下, 心肌细胞外的钾离子浓度是变化的, 钾离子的横向扩散会导致细胞外钾离子的聚集和产生钾扩散耦合, 用考虑钾扩散耦合的Luo-Rudy相I心脏模型研究了钾扩散耦合对螺旋波动力学的影响. 数值模拟结果表明: 当钾扩散耦合比较强时, 钾扩散耦合使细胞外钾离子浓度先升高, 然后做规则振荡, 导致螺旋波做无规则漫游; 观察到螺旋波的波臂宽度和频率随钾扩散耦合的强度增大而减小, 这样, 当钾扩散耦合足够强时, 钾扩散耦合可以消除螺旋波和时空混沌. 关键词： 钾扩散耦合 螺旋波 时空混沌     

A comparison of ion scattering spectra and molecular dynamics simulations at the surface of silicate glasses

Molecular dynamics simulations are correlated with experimental ion scattering spectra to elucidate the surface structure and composition of fused silica and potassium trisilicate glass. The ion scattering spectra and molecular dynamics simulations both show that the oxygen atoms dominate the surface monolayer of fused silica. The ion scattering spectra of fracture surfaces of potassium trisilicate glass show a large potassium signal with little scattering signal from the oxygen or silicon atoms indicating a predominance of potassium in the surface monolayer. This local enrichment of potassium in the surface monolayer is due to their shielding of the charged silicate tetrahedra at the surface. This is also consistent with the simulations.     

A TDS and HREELS study of CO adsorbed on a potassium promoted Fe(111) surface

The adsorption behavior of CO on a potassium promoted Fe(111) surface was investigated in the range from zero to several monolayers of preadsorbed potassium. TD spectra show that the presence of potassium decreases the amount of CO which is desorbed in the α (molecular) desorption state and increases the desorption temperature of this state. In addition, it gives rise to second, β (recombination) desorption state which is correlated to K desorption. The total CO uptake is comparable to that for the clean surface for precoverages of up to one monolayer, beyond this, however, it increases and at three potassium monolayers it is about twice the clean surface value. At K precoverages above 0.5 monolayer the initial sticking coefficient for CO is greatly reduced so that CO exposures of up to several thousand Langmuirs are required in order to saturate the surface. The three stretch frequencies which are observed in HREELS for CO adsorbed on clean Fe(111) are all affected by the presence of potassium. At potassium precoverages between zero and 0.5 monolayers these frequencies shift both in energy and relative intensity; however, between 0.5 and 1 preadsorbed potassium monolayers the spectra are greatly modified and now show only two losses in the CO stretch region. The lower-frequency one of these gives evidence for a close interaction of CO with the coadsorbed potassium.     

Potassium adsorption on Fe(110)

LEED, AES, UPS and XPS were used to study submonolayer coverages of potassium on Fe(110). At room temperature the maximum potassium coverage is characterized by a LEED superstructure. This LEED pattern is interpreted as being due to a hexagonal close-packed K layer on Fe(110), resulting in a maximum atom density of 5.3 × 10¹⁴ cm^?2, i.e.θ k = 0.31. The work function change and the shift of the K(2p) and K(3p) core levels with potassium coverage indicate a charge transfer from potassium to iron at low potassium coverages.     

Substitutional adsorption of K on Fe(100)

The adsorption of potassium on Fe(100) was studied by time-of-flight forward scattering and recoiling spectroscopy (TOF-SARS), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). After heating to 650 K of the potassium saturated surface the formation of a p(3 × 3) potassium superstructure was observed by LEED. TOF-SARS experiments ruled out the adsorption of potassium in the on-top, bridge and four-fold hollow site. The only site which is in agreement with all experimental results is the substitutional site where K replaces an Fe atom of the topmost layer of the crystal. This is the first time a substitutional adsorption site has been found on a bcc surface. On an fcc surface such an adsorption site has been found recently for adsorption of sodium and potassium on Al(111).     

Potassium-induced activation of field emitters with fullerene coating

The influence of potassium deposition on the emission characteristics of field tip emitters with fullerene coatings is studied. It is shown that a three-to fourfold reduction of the typical voltage U ₁ required for the given emission current can be attained by rapid deposition of potassium layer with a thickness exceeding a monolayer. The deactivation of emitters at room temperature in the absence of electric field is observed and studied. Presumably, the deactivation is caused by potassium redistribution within the coating and/or the formation of bonds between potassium atoms and fullerene molecules. Deactivation of this type actually comes to an end in one or two days. The deposition of potassium on fullerene coating results in an appreciable (up to 50%) decrease in U ₁ of the field emitters even after their long-term (about five days) deactivation.     

WOx phase growth on SiO2/Si by decomposition of tungsten hexacarbonyl: Influence of potassium on supported tungsten oxide phases

Synchrotron based photoemission spectroscopy was used to study the adsorption of tungsten hexacarbonyl on SiO₂ surfaces modified by potassium. Results were compared with the ones obtained when no potassium was present. Experiments using W4f and Si2p intensities variations show that, at 140 K, the tungsten hexacarbonyl growth proceeds via a simultaneous multilayer mode for the two kinds of surfaces but with differences in compositions of growing layers. Indeed, it is evidenced that, even at cryogenic temperatures, the presence of potassium induces decomposition of a significant part of tungsten hexacarbonyl molecules through a strong interaction between tungsten and potassium atoms in opposition to potassium-free surface cases where W(CO)₆ molecules are simply physisorbed. Additional irradiation of adsorbed molecules with photons coming from 0-order synchrotron radiation, subsequent going back to room temperature and additional thermal treatments up to about 700 K were then used to induce further decomposition of the adsorbed precursor. It allows as well to get rid of carbon and, finally, to stabilize different W-based species on the surface. The state of tungsten remaining on the surface is then strongly influenced by presence of potassium. When potassium is present, highly oxidized tungsten species are observed, whereas reduced species are mainly detected for potassium-free surfaces. Moreover, as diffusion of potassium is revealed during formation of tungsten phase, one should guess that potassium plays a crucial role in tungsten oxidation mechanism.