Intramolecular coupling between non-penetrating high molecular Rydberg states

摘要

We address a central question in the realm of the dynamics of high-n (= 40-250) Rydberg states of diatomics and large molecules. What is the coupling responsible for the ' global' l mixing, which results in the breakdown of the n~3 scaling law for the non-radiative lifetimes and for the lifetime lengthening (by two to four orders of magnitude) of these states? To explore the implications of intramolecular interactions on l mixing and on electronic-rotational energy exchange we analysed the intramolecular couplings of the ion core dipole, quadrupole and (anisotropic) polarizability with a non-penetrating (l ≥ 3) Rydberg electron, in conjunction with the energy gaps between proximal pairs of energy levels. Calculations of the energy gaps and the couplings were performed for the high-n non-penetrating Rydberg states of NO and for model 'light' (B = 19 cm~(-1)) and 'heavy' (B = 0.05 cm~(-1)) polar molecules. All the intramolecular interactions are of the form of a power law proportional to l~(-n), with η being determined by the nature of the long-range coupling, by the l dependence of the quantum defects for multipole couplings and by the l dependence of angular integrals. We established a bottleneck effect for the intramolecular couplings between non-penetrating (l ≥ 3) states. For n- and N~+-changing dipole, quadrupole and polarizability interactions the energetics of the proximal pairs of levels, in conjunction with the bottleneck effect, prohibit the |n,l,N~+,N > -|n′l′,N~+′,N > , l ( ≥ 3) couplings (with n ≠ n′) and the electronic-rotational energy exchange. For n- and N~+ -conserving quadrupole and polarizability interactions, the l ( ≥ 3) mixing (which prevails only for l ≤ N~+ + N) is also prohibited by the bottleneck effect.' Global' intramolecular l mixing (with both n ≠ n′ and n = n′) in diatomics and in large molecules is precluded, implying that the dramatic lengthening of the non-radiative lifetimes of high-n Rydberg states can be induced only by exterior electric field coupling.