物理化学学报 >> 2004, Vol. 20 >> Issue (08S): 1010-1016.doi: 10.3866/PKU.WHXB200408zk18

综述 上一篇    下一篇

分子单重/叁重混合激发态碰撞传能中的量子干涉效应

沙国河;张存浩   

  1. 中国科学院大连化学物理研究所分子反应动力学国家重点实验室,大连 116023
  • 收稿日期:2004-03-23 修回日期:2004-03-29 发布日期:2004-08-15
  • 通讯作者: 沙国河 E-mail:ghsha@dicp.ac.cn

Quantum Interference Effect in Collision-induced Intramolecular Energy Transfer within Singlet-triplet Mixed States

Sha Guo-He;Zhang Cun-Hao   

  1. State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023
  • Received:2004-03-23 Revised:2004-03-29 Published:2004-08-15
  • Contact: Sha Guo-He E-mail:ghsha@dicp.ac.cn

摘要: 量子干涉效应是基于量子力学波粒二象性原理,即微观粒子的运动皆具有波的特性而产生的一种干涉现象,故又称为物质波干涉.近年来,在分子的光激发、光解和光电离及碰撞过程中皆已观察到量子干涉效应,成为分子动态学领域研究热点之一.我们小组在国际上首次得到了单重/叁重混合激发态分子碰撞传能中的量子干涉的实验证据,从理论上导出了包括干涉相位角的传能截面公式,从实验上发展了激光双共振多光子电离光谱技术,用以测定了CO(A 1Π,v=0/e 3Σ-,v=1)与各种原子(He, Ne, Ar)及双原子分子H2, O2, N2, HCl碰撞传能的干涉角.其后又与李丽的小组合作,在热管炉中用激光双共振诱导荧光法观察到Na2(A 1Σu+, v=8/b 3Π0u, v=14)-Na碰撞中的量子干涉效应,证明了碰撞干涉效应的普遍性.近年来,在理论方面,我们发展了基于含时微扰的一级波恩近似量子散射方法,计算出了上述碰撞体系的干涉角θST,与实验值符合极好.本文指出虽然气池实验测得的干涉角θST是不同分子碰撞速度及碰撞参数的“平均”结果,但与理论计算的微分干涉角尚比较接近,可提供激发态分子碰撞相互作用势的重要而难得的信息.

关键词: 单重-叁重混合态, 碰撞传能, 量子干涉, 光学双共振多光子电离

Abstract: The principle of wave-particle duality of quantum mechanics ascertains that any microscopic particle must also exhibit wave properties. The matter wave, or de Broglie wave, was first evidenced by Davisson and Germer in 1927 in the electron diffraction by crystals. In recent years, numerous fascinating examples of the quantum interference effect (QIE) have been discovered in the molecular systems in their excitation, dissociation and ionization by photons as well as in collision processes. Our group was the first to obtain the experimental evidence of QIE in a collision, specifically for the singlet-triplet mixed state of a diatomic species, and to derive an explicit expression for its energy transfer cross-section. In this expression, the interference phase angle (θST) that describes the phase angle difference between singlet and triplet energy transfer channels is defined and experimentally measured for CO(A 1Π,v=0/e 3Σ-,v =1)-M collision system with M= rare gases (He, Ne, Ar), homonuclear diatomics (H2, N2, O2) and heteronuclear diatomics (HCl) via the optical-optical double resonance multiphoton ionization (OODR-MPI) technique. We have also observed QIE in Na2(A 1Σu+, v=8/b 3Π0u, v =14)-Na collision. More recently, we have carried out quantum scattering calculations of the interference angle based on the first order Born approximation of time dependent perturbation theory. For atom-diatom collision,the anisotropic Lennard-Jones interaction potential was adopted, and for polar diatom-diatom collision, the long-range dipole-dipole interaction proportional to R-3 was shown to be a proper potential for the calculation. All the calculated θST at T=77,253 and 470 K for CO(A 1Π,v=0/e 3Σ-, v =1)-M, for M=He(θST=58°~65°), Ne(66°~69°), Ar(72°~90°) and HCl(101°~110°), are in good agreement with the experiments. Our calculated differential θST are in the range of 48°~70° for CO-He and 93°~112° for CO-HCl collision for all v and b values that are physically significant. These values are close to those experimental θST′s obtained in the gas cell, implying that the “average effect” is not serious. The calculation also gives an effective collision time of 0.3 ps for CO-He and 1.5 ps for CO-HCl collision, which explains why the experimental θST for the former is much smaller than that of the latter. These results show that θST should provide important information on the singlet-triplet mixed state intermolecular potential, which is difficult to obtain by other experimental or theoretical methods.

Key words: Singlet-triplet mixed state, Collisional energy transfer, Quantum interference, Double resonance multiphoton ionization