Comparing momenta and pi-electron energy of benzenoid molecules

Let G be a graph associated with the hexagonal system of a benzenoid hydrocarbon. Let @l"1=<...=<@l"n be the set of eigenvalues of the adjacency matrix of G and consider the momenta M"[email protected]?"i"="1^[email protected]"i^k for k even. We show the lower bound M"q^2(M"rM"s)^-^1^/^2=