Anomalous nitrogen isotope ratio in comets

High-resolution spectra of the CN B-2 Sigma(+)- X-2 Sigma(+) (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 C-12/C-13, 140 +/- 35 and 140 +/- 30 for N-14/N-15. Our N isotopic measurements are lower than the terrestrial N-14/N-15 = 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.