铷原子簇自发磁矩的实验观测及理论分析

Experimental observation and theoretical analysis of spontaneous magnetic moment of Rb atom clusters

在碱金属原子簇磁性的研究中,存在自由原子簇含有的原子个数及其磁矩难以准确确定的问题,本文采用光磁共振光谱检测手段,对工作温度约为328 K的饱和铷蒸汽样品中单原子分子^(87)Rb_(1)和14种簇粒子(^(87)Rb)n’(n’=2,3,…,15)的磁矩进行了深入研究.实验结果表明:在同一外磁场下,14种簇粒子(^(87)Rb)n’,的共振频率fn’与^(87)Rb_(1)的共振频率f*之间存在fn’=f*/n’的数值关系,并且各簇粒子的磁矩值与振幅值均随n’的大小和奇、偶性呈现不同性质的变化规律.运用分子轨态理论通过^(87)Rb_(n)=^(87)Rb_(n)-1+^(87)Rb联合原子簇构造模式,给出14种簇粒子^(87)Rb_(n)(n=2,3,…,15)的基态和最低激发态的电子组态和分子态项型,分析了各分子态的稳定性和发生可见塞曼效应的可能性.进一步基于双原子分子磁矩公式计算,发现当n=n’时^(87)Rb_(n)的磁矩值与(^(87)Rb)n’的磁矩值严格吻合(平均相对误差仅为0.6765%),证实了(^(87)Rb)n’和^(87)Rb_(n)的对应关系.

For the magnetism of alkali metal clusters,it is difficult to determine the number of atoms and the magnetic moment of isolated atoms cluster.In this paper,we investigate the magnetic moment of single atomic molecule^(87)Rb_(1)and 14 kinds of cluster particles(^(87)Rb)n’(n’=2,3,4,…,15)in a saturated rubidium vapor sample at about 328 K,by using optical magnetic resonance spectroscopy.The experimental results show that there is a relationship fn’=f*/n’between the resonant frequencies fn’of 14 kinds of cluster particles(^(87)Rb)n’and the resonant frequencies f*of^(87)Rb_(1).The magnetic moment and their resonance amplitudes show two different relationships with the n’odevity.When the particles have an odd number of 5 s electrons,they must have spontaneous magnetic moment,and the value of magnetic moment increases with n and decreases inverse proportionally with the combined angular momentum F of the cluster particles.The amplitude obtained from resonance spectrum complies with the variation law of magnetic moment value.On the other hand,for the cluster particles with n being even number,the magnetic moment value becomes 0 and the amplitude is also 0 in the most cases,except for the cluster particles^(87)Rb2 with n=2 i.e.two 5s electrons,which is caused by the Jahn-Teller effect of the linear molecules,and the magnetic moment value is consistent with the calculation results of the odd number particles.When n>2,the coupling effect between the magnetic moments of the Rb cluster shows a long-range ordered antiferromagnetic property with the increase of the number of 5s valence electrons n.The electron configuration and molecular state of the ground state and the lowest excited state of 14 kinds of 2—15 atoms cluster particles^(87)Rb_(n),as well as the stability of each molecular state and the possibility of visible Zeeman effect are obtained by using the molecular orbital-state theory analysis and constructing the^(87)Rb_(n)1+87 Rb_(n)atomic cluster model.Furthermore,based on the magnetic moment of diatomic molecules ruler,it is found that when n=n’,the magnetic moment of(^(87)Rb)n’and^(87)Rb_(n)are in strict consistency(the average relative error is only 0.6765%),confirming the corresponding relationship between(^(87)Rb_(n)’and^(87)Rb_(n).This research will be of great value in the magnetic research of cluster particles.