Iterative eigenvalue method using the Bloch wave operator formalism with Padé approximants and absorbing boundaries.

We present an iterative method for calculating eigenvalues and eigenvectors of large non-Hermitian matrices. The method uses an iterative procedure to solve the basic Bloch equation HOmega=OmegaHOmega of wave operator theory. It involves nonlinear transformations such as the translation of diagonal matrix elements in the complex plane and the use of Padé approximants to treat the strongly coupled states which constitute an intermediate space around the model space. In the particular case of Floquet eigenstates the further step of adding time-dependent absorbing boundaries significantly improves the convergence properties of the iterative calculations.

Anomalous nitrogen isotope ratio in comets.

High-resolution spectra of the CN B2 summation operator +-X2 summation operator + (0,0) band at 390 nanometers yield isotopic ratios for comets C/1995 O1 (Hale-Bopp) and C/2000 WM1 (LINEAR) as follows: 165 +/- 40 and 115 +/- 20 for 12C/13C, 140 +/- 35 and 140 +/- 30 for 14N/15N. Our N isotopic measurements are lower than the terrestrial 14N/15N = 272 and the ratio for Hale-Bopp from measurements of HCN, the presumed parent species of CN. This isotopic anomaly suggests the existence of other parent(s) of CN, with an even lower N isotopic ratio. Organic compounds like those found in interplanetary dust particles are good candidates.