Na2高位振动态与Ar，N2碰撞中模温度的变化

利用受激发射泵浦激发Na2分子,使Na2 得到布居,研究了高振动激发态Na2*与Ar和N2的碰撞弛豫过程。由激光诱导荧光得到Na2 各振动能级的时间分辨布居分布,从而得到Boltzmann振动温度和转动温度随时间的变化。对于Na2*与Ar碰撞,在泵浦-探测延迟时间tD=8μs前,振动温度Tvib减小很慢;在8-12μs间,Tvib迅速下降并达到平衡。而转动温度Trot和平移温度Ttran在Tvib迅速下降时才开始缓慢增加。对于Na2*与N2碰撞,Tvib存在三个变化阶段,先是迅速下降,然后下降减缓,最后减小很慢并达到平衡。而在整个过程中,Trot和Ttran一直是很缓慢地增加。实验数据说明了弛豫过程是分阶段进行的,单一速率系数不能正确解释复杂的弛豫过程,并会丢失平衡过程中的关键特点。     

Na_2高位振动态与Ar,N_2碰撞中模温度的变化

利用受激发射泵浦激发Na2分子,使Na2[X1∑+g(ν″=33,J″=11)]得到布居,研究了高振动激发态Na*2与Ar和N2的碰撞弛豫过程.由激光诱导荧光得到Na2(ν≤33)各振动能级的时间分辨布居分布,从而得到Boltzmann振动温度和转动温度随时间的变化.对于Na*2与Ar碰撞,在泵浦-探测延迟时间tD=8μs前,振动温度Tvib减小很慢;在8-12μs间,Tvib迅速下降并达到平衡.而转动温度Trot和平移温度Ttran在Tvib迅速下降时才开始缓慢增加.对于Na*2与N2碰撞,Tvib存在三个变化阶段,先是迅速下降,然后下降减缓,最后减小很慢并达到平衡.而在整个过程中,Trot和Ttran一直是很缓慢地增加.实验数据说明了弛豫过程是分阶段进行的,单一速率系数不能正确解释复杂的弛豫过程,并会丢失平衡过程中的关键特点.     

高振动激发Na2与Ar,H2的碰撞弛豫

受激发射泵浦(SEP)激发Na2(X1Σ+g)的(v=33~51,J=11)高位振动态,利用激光诱导荧光(LIF)光谱研究了Na2(X)高位振动态分别与Ar和H2的碰撞能量转移过程。SEP布居的高位态粒子的衰减曲线是一纯指数函数,由此得到总碰撞转移速率系数,它们随振动能级的增加而线性增加。测量从νp=48,Jp=11转移到(47,J)态上布居的LIF光强的相对强度,得到相对转移速率系数,再由总转移速率系数得到态—态转移的绝对速率系数。对于Na2(ν)+Ar,多量子弛豫没有观察到。对于Na(ν=48)+H2,由泵浦得到的高位态ν=48上的布居的相当大的部分直接弛豫到较低能级ν=43(Δν=-5),所用的弛豫时间比位于ν=48和43中间的态之间的碰撞时间还要短,故相继单量子弛豫的机制可消除。对于ν=48,至少有占其布居数的40%的粒子经历了多量子振动弛豫过程,对这种过程的可能机制进行了讨论。     

振动激发KH与CO_2碰撞中能量的时间分辨分布

K(5P)与H2反应产生KH(Х1Σ+)的ν″=0~3振动能级,泛频激发KH至ν″=17高位振动态。通过测定KH(ν″=17,3)与CO2碰撞过程中振动能的时间分辨分布(即Tν的变化过程),研究了高低振动态碰撞传能的不同特点。对于KH(ν″=17),振动温度Tν的变化分为三个阶段:第一阶段(0~5μs)Tν迅速下降,能量应主要转移至CO2(0001)振动态或(0000)高位转动态;第二阶段(5~20μs)Tν仅稍有下降,向CO2振动态及高位转动态的能量转移已结束;第三阶段(20μs后)Tν虽然缓慢但明显下降,表明向CO2低转动态及平动能的转移加速。对于KH(ν″=3),Tν的变化只分为两个阶段:第一阶段(0~10μs)的共振V-R过程迅速降低了振动温度;第二阶段(10~80μs)Tν有一个缓慢下倾,只能转移到很低的转动态和小的平动能。这些结果表明了振动激发态分子与基态分子碰撞中仅用单一速率系数不能正确揭示复杂平衡过程的本质,不同的阶段应该用不同的速率系数来描述。利用瞬时吸收技术得到CO2(0000)和(0001)的原生态转动布居分布,通过速率方程分析,得到平衡过程中不同阶段的速率系数。     

H_2(v=1)与CO_2碰撞中CO_2的振动和转动激发

利用高分辨率瞬时激光光谱技术,研究了H2(1,1)与CO2碰撞中的能量转移。受激拉曼泵浦把H2(0,1)激发到H2(1,1)能级,H2(1,1)与CO2碰撞,使CO2的振转态得到布居,通过泛频吸收得到CO2(0000)和(0001)的转动态分布,测量H2(0,1)和H2(1,1)的CARS(相干反斯托克斯拉曼散射)谱,得到这二个能级布居数密度之比,而H2(0,1)密度通过在池温300K下H2(v=0)的转动Boltzmann分布得到。碰撞转移速率系数由一个速率方程得到,对于CO2(0000)J=48~76,速率系数ktr从(3.9±0.8)×10-11单调递增到(1.4±0.3)×10-10 cm3·molecule-1·s-1,而对于(0001)J=5~33,速率系数均在(4.3±0.9)×10-12cm3·molecule-1·s-1附近。随H2(1,1)的激发,在0.5μs内测量CO2(0000)和(0001)原生态的转动布居,得到玻尔兹曼转动温度Trot,对于(0000)态,有Trot=1 100K,对于(0001)态有Trot=310K,与池温接近。利用泛频吸收线的多普勒增宽测量,得到CO2各转动态的实验室平移温度Ttran和质心平移温度Trel,对于(0000)J=48和76,Trel分别为454和1 532K,平动能平均变化在231~1 848cm-1之间,而对于(0001)J=5~33,平均平动能基本无变化。     

CsH(X1∑+,v≥15)与CO2碰撞中的振动-转动能量转移

研究了高位振动激发态CsH(v"=15～21)与CO2振动-转动碰撞转移过程.脉冲激光激发CsH至高振动态,利用激光感生荧光光谱(LIF)得到CsH(v")与CO2的猝灭速率系数kv"(CO2),kv"＝21(CO2)＝7kv"＝15(CO2).研究了CsH(v")+H2的弛豫过程,有kv"(H2)＞kv"(CQ),碰撞弛豫速率系数的质量效应明显.利用激光泛频光谱技术,测量了CO2(00°0)的转动态分布.对于CO2与CsH(v"=15)碰撞,CQ2有转动温度Trot=(605±50)K;对于v"=21,Trot=(780±70)K.基于转动温度,得到CO2的平均转动能〈Erot〉和转动能的变化〈ΔErot〉,发现〈ΔErot〉v"=21～2.7〈△Erot〉v"=15.由对CO2转动能级受激吸收线轮廓测量,得到J=36～48各能级的平均平动能〈Etel〉,对于v"＝15,〈Erel〉＝600～972 cm-1;对于v"=21,〈Erel〉=972～1351cm-1.低J值有低平动能.外推平动能到初始平动能520 cm-1(池温500 K的平动能)对于v"＝15和v"＝21,分别得到阈值Jth =34和24.大于初始平动能的转动态均处于Jth值之上.     

HBr(X~1Σ~+ν~″=5)分子与H_2,N_2,CO_2和HBr间的近共振振动-振动能量转移

利用简并受激超拉曼泵浦激发HBr(Χ~1Σ~+ν~″=5)振动态,由高分辨瞬时激光感应荧光(LIF)探测碰撞弛豫后HBr(ν~″≤5)各振动态时间分辨布居数的演化过程,得到了HBr(ν~″=5)分别与分子M(H_2,N_2,CO_2和HBr)的碰撞弛豫速率系数。对于M=CO_2,近共振的1-1振动-振动(V-V)能量转移是有效的,这一结果表明CO_2强的红外振动模对近共振V-V能量转移是有利的。而红外禁戒跃迁的N_2(0-1)的近共振V-V转移虽然也能观察到,但相应速率系数比CO_2小2个量级。碰撞分子的振动跃迁红外活性越强,能量转移速率系数越大。在HBr(ν~″=5)+HBr的自弛豫过程中,单量子弛豫率占总弛豫率的70%,而双量子弛豫约占25%。在HBr(ν~″=5)+H_2中,只有2-1的V-V近共振过程是重要的。同时还研究了V-V近共振能量转移速率系数与温度变化的关系,对于CO_2的1-1近共振,V-V能量转移速率系数随温度的增加而减小;对于H_2和HBr,其弛豫速率系数随温度的增加而增加;对于N_2,其弛豫速率系数随温度的增加而缓慢增加。     

高激发振动态RbH（Х1Σ+,ν″=15～22）与H2,N2的振动-振动碰撞能量转移

脉冲激光激发Rb原子至6 D态,Rb(6 D)与H2反应生成RbH(Х1Σ+,ν″=0～2)振动态。研究了RbH(Х1Σ+)高位振动态与H2,N2间的碰撞弛豫过程,利用泛频泵浦分别激发Х1Σ+(ν″=0)至Х1Σ+(ν″=15～22)各振动态,检测激光激发Х1Σ+(ν″)至A1Σ+(ν′),测量A1Σ+(ν′)的时间分辨激光感应荧光光谱,利用Stern-Volmer方程,得到振动能级ν″的总的弛豫速率系数kν(H2)。在H2和N2的混合气体中,总弛豫速率系数kν(H2+N2)与α(H2的摩尔配比)成直线的关系,其斜率为kν(H2)-kν(N2),而截距为kν(N2)。对于ν″<18主要发生单量子弛豫(Δν=1)过程,kν(H2)和kν(N2)与振动量子数ν″均成线性增加关系。对于ν″≥18,多量子弛豫(Δν≥2)过程及共振振动-振动转移起重要作用。对于RbH(ν″=21)+N2(0),测量ν″=16的布居数时间演化轮廓,在20μs内有一个锐锋,在100～200μs内有一个较低的宽峰,锐锋相应于RbH(ν″=21)+N2(0)→RbH(ν″=16)+N2(1)的共振转移过程,而宽峰是由相继的单量子过程产生的。     

高振动激发态DBr(X~1Σ~+,v″=8、7)与 D_2,Ar间的碰撞振动能量转移

利用YAG激光器泵浦OPO激光简并受激超拉曼泵浦DBr分子至基电子态的高振动态v″=8、7,研究高振动态DBr分子与其他碰撞气体(Ar、D_2)的碰撞弛豫过程.对于DBr(v″=8)和Ar、D_2混合体系,由高分辨瞬时激光感应荧光光谱方法探测碰撞弛豫后DBr分子振动态v″=8的时间分辨布居数的演化过程.保持总压强不变,改变碰撞气体的摩尔配比,测量相应条件下的有效寿命,由混合气体系统中Stern-Volmer公式,得到DBr(v″=8)分子与Ar、D_2的碰撞弛豫速率系数分别为k_8(Ar)=(0.51±0.1)×10~(-12 ) cm~3molecule~(-1)s~(-1),k_8(D_2)=(3.50±0.8)×10~(-12) cm~(3 )molecule~(-1 )s~(-1);DBr(v″=8)分子的平均自弛豫速率系数为k_8(DBr)=(1.20±0.4)×10~(-12) cm~3molecule~(-1)s~(-1).对于摩尔配比为0.5的DBr和D_2混合体系,Ti宝石激光器分别双光子激发DBr v″≤8、7各振动态至第一电子激发态A~1Πv′态,测量各个振动态的荧光光强随时间演化,测量结果表明DBr (v″=8、7)与D_2的碰撞弛豫中均发生了二量子弛豫;对于摩尔配比为0.4的DBr(v″=8)和Ar混合体系,只有连续单量子碰撞弛豫过程.     

CO_2与高振动激发K_2碰撞中的全分辨转动态分布

在K_2+CO_2中,受激发射泵浦得到K_2(E=3 500和4 000cm~(-1))高位振动态,研究了高振动激发K_2与CO_2碰撞产生的CO_2全分辨转动态分布。利用高分辨瞬时激光诱导荧光(LIF)测量了CO_2(0000)J=2~74的转动和平移能量轮廓,利用双高斯函数拟合,分别确定各转动态的产生和倒空线宽,从而得到碰撞产生的Doppler展宽、平移温度和平移能。对于K_2不同的激发能E,能量转移的机制是相似的,为振动-转动/平移弛豫机制。但碰撞出现部分的平移温度均超出池温,而碰撞倒空部分的平移温度均略低于池温,平移能随E的增加而增大,E增加14%,平移能增加40%。CO_2(0000)转动态分布的半对数描绘给出了双指数分布,对于K_2E=3 500cm~(-1),低J态分布T_a=(523±60)K,高J态分布T_b=(1 890±210)K。Ta接近池温,说明低J态为近弹性碰撞,属单量子弛豫过程,而高J态为非弹性碰撞,属多量子驰豫过程。对于K_2E=4 000cm~(-1)同样有双指数行为,低J分布T_a=(620±65)K,高J分布T_b=(2 240±250)K。高振动态K_2(E)与CO_2碰撞,E=4 000cm~(-1)比E=3 500cm~(-1)的Ta和Tb均约高19%,说明转动分布对于K_2不同能量是敏感的,但弹性和非弹性分支比是基本相同的,弱碰撞约占82%,强碰撞约占18%。     

Magnetic ordering in HoRu2Si2, HoRh2Si2, TbRh2Si2 and TbIr2Si2 by neutron diffraction

Neutron diffraction study of polycrystalline HoRu₂Si₂, HoRh₂Si₂, TbRh₂Si₂, and TbIr₂Si₂ was performed in the temperature range between 4.2 and 300 K. For HoRu₂Si₂ the magnetic spin alignment of a linear transverse wave mode below the Néel temperature 19 K is observed. This static moment wave is propagating along the b-axis with k=(0, 0.2, 0) and is polarized in the c-axis. The root-mean-square and maximum saturation moments per Ho atom are 9.26 and 13.09μ_B, respectively. HoRh₂Si₂, TbRh₂Si₂ an TbIr₂Si₂ are simple collinear antiferromagnets of +-+- type with Néel temperatures of (27±1), (98±2) and (72±3) K, respectively. For TbRh₂Si₂ and TbIr₂Si₂ magnetic moments are localized on RE ions only and are aligned along the tetragonal axis, while for HoRh₂Si₂ they form an angle ø = (28±3)°.     

13C-selective IRMPD of CBr2F2/Cl2 and CCl2F2/Br2 systems

The CO₂ TEA laser irradiation of CBr₂F₂ in the presence of Cl₂ yielded ¹³C-enriched CBrClF₂ and ¹³C-enriched CCl₂F₂ under selected experimental conditions. As the photolysis proceeded, the ¹³C concentration of CBrClF₂ decreased gradually and that of CCl₂F₂ increased up to 90% or higher. These results can be explained by the mechanism involving the secondary ¹³C-selective IRMPD of the primary product CBrClF₂. On the other hand, the carbon-containing product for a CCl₂F₂/Br₂ system was only CBrClF₂; the further IRMPD of which probably regenerated CBrClF₂ in the presence of Br₂. The decomposition probabilities of ¹²C- and ¹³C-containing molecules in both systems were measured as functions of laser line, laser fluence, and reactant pressures.     

μ+SR study of LaNi2As2, URh2Si2 and CeRh2Si2

Muon spin relaxation experiments have been carried out in the paramagnetic and magnetically ordered states of URh₂Si₂ and CeRh₂Si₂. As the magnetic structure of these compounds is well known, these measurements can help to characterise their magnetic properties probed by μSR and to understand the μSR results of the heavy fermion compounds of the same crystallographic family. Our measurements show that the muons occupy two different crystallographic sites. The spectra of URh₂Si₂ and CeRh₂Si₂ in the magnetically ordered states are very different, probably reflecting their different magnetic structures. The spectra obtained on CeRh₂Si₂ are similar to the published spectra of the heavy fermion compound CeCu_2.1 Si₂. Muon spin rotation measurements on LaNi₂As₂ indicate that the muon is diffusing at 150 K.     

Eu2+掺杂CaSi2O2N2荧光粉发光性能

采用固相反应法合成了组成为Ca_1-xEu_xSi₂O₂N₂的Eu²⁺掺杂CaSi₂O₂N₂荧光粉.通过荧光光谱对样品的发光性能进行了研究,发现Eu²⁺掺杂CaSi₂O₂N₂荧光粉发射光谱为宽波段的单峰结构,主要包含绿光和黄光区,发射峰在556~568 nm.从发射光谱的宽带特征来看,CaSi₂O₂N₂:Eu²⁺的发射主要对应着Eu²⁺离子4f⁶5d→4f⁷跃迁.从激发光谱所覆盖的范围还可以看到,样品可以有效的被UV蓝-光激发,这意味着该类荧光粉在白光LED方面有可能得到广泛的应用.另外,样品的发光性能与激发离子的浓度有着很大关系.激发离子浓度增大时,发射光谱会发生明显红移.利用这一性质,可以通过改变Eu²⁺浓度来调节荧光粉的发光范围,从而满足不同场合的需要.同时,Eu²⁺浓度提高,样品发射光谱的强度也会随之增强,在x=0.06时发射强度达到最大值,之后继续增加Eu²⁺浓度,强度不仅没有增加反而降低,即出现浓度猝灭现象.     

Polar optic phonons in Hg2Cl2 and Hg2Br2

Far infrared (30–430 cm^?1) reflectivity measurements of Hg₂Cl₂ and Hg₂Br₂ single crystals have been performed in polarized light. The spectra, which are in agreement with group-theoretical predictions, were analyzed by the oscillator fitting procedure and Kramers-Kronig method. The results are compared with the existing data from other measurements and the large anisotropy of polar modes is briefly discussed. The polarization vectors of all long-wavelength symmetry modes were determined group-theoretically.     

Magnetostriction of SmMn2Ge2 and GdMn2Ge2 intermetallic compounds

Longitudinal and transverse magnetostrictions of polycrystalline samples of intermetallic compounds RMn₂Ge₂ (R=Sm or Gd) are measured in pulsed magnetic fields up to 250 kOe. It is found that linear magnetostrictive strains of about 10^?3 arise in a temperature range in which the magnetic field causes a change in the magnetic state of a manganese magnetic subsystem. The results obtained are described within the model of a two-sublattice ferrimagnet with a negative exchange interaction in the manganese subsystem in terms of a strong dependence of this interaction on interatomic distances.     

Superconductivity in LaPd_2Bi_2 with CaBe_2Ge_2-type structure

正Since the discovery of superconductivity in LaFeAsO_(1-x)F_x,the high-T_c iron-based superconductors have been extensively studied from both experimental and theoretical viewpoints [1-8]. However, the mechanism of the unconventional superconductivity is still to be resolved. To     

X-ray photoemission spectra measurements of CeNi2Sb2 and CeCu2Sb2

X-ray photoemission spectra, resistivity and susceptibility of CeNi₂Sb₂ and CeCu₂Sb₂ were measured and are discussed. The results indicate that these alloys are Kondo systems. For comparison of the valence band properties, the spectra of the isostructural alloys of RT₂X₂-type with R = La, Gd, T = Cu, Ni and X = Sn, Sb were investigated, too.