Acta Phys. -Chim. Sin. ›› 2004, Vol. 20 ›› Issue (08S): 1010-1016.doi: 10.3866/PKU.WHXB200408zk18

• Review • Previous Articles     Next Articles

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

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