INTRAMOLECULAR COUPLING BETWEEN NONPENETRATING HIGH-MOLECULAR RYDBERGSTATES

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 t hese states? To explore the implications of intramolecular interaction s 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 greater than or equal to 3) Rydberg electron, in conjunction with the energy gaps betw een proximal pairs of energy levels. Calculations of the energy gaps a nd 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 o f the form of a power law proportional to l(-n), with eta being determ ined by the nature of the long-range coupling, by the l dependence of the quantum defects for multipole couplings and by the I dependence of angular integrals. We established a bottleneck effect for the intramo lecular couplings between non-penetrating (l greater than or equal to 3) states. For n- and N+-changing dipole, quadrupole and polarizabilit y interactions the energetics of the proximal pairs of levels, in conj unction with the bottleneck effect, prohibit the \n, l, N+, N]-\n', l' , N+', N], l (greater than or equal to 3) couplings (with n not equal n') and the electronic-rotational energy exchange. For n- and N+-conse rving quadrupole and polarizability interactions, the l (greater than or equal to 3) mixing (which prevails only for l less than or equal to N+ + N) is also prohibited by the bottleneck effect. 'Global' intramo lecular l mixing (with both n not equal n' and n = n') in diatomics an d in large molecules is precluded, implying that the dramatic lengthen ing of the non-radiative lifetimes of high-n Rydberg states can be ind uced only by exterior electric held coupling.