Dear Editor: I intend to submit a report to Science. We did three new things in the paper. First, we modeled the photodissociation of O2 isotopologues in the mesosphere. Second, we explained the remarkable measurements of Thiemens. This result offers a beautiful solution for the change in slope in Thiemens’ data at the highest altitudes of his measurements (Science 270, 969, 1995), which have remained a challenge to atmospheric science for a decade. Third, we showed testable consequences of our model which can serve to motivate new measurements. My colleagues Mimi Gerstell, Mark Allen, Andy Ingersoll, Chip Miller, Xun Jiang and Hy Hartman have read the paper. If the paper is accepted. I wish to see it published back to back with a related paper that has been submitted to Science "Extraordinary Isotopic Fractionation in Ozone Photolysis" by Miller et al. Manuscript Number:1109969 Without exaggeration, these two papers are the greatest modeling papers on oxygen isotopes in the middle atmosphere after Gao and Marcus (Science 293, 259, 2001), whose work only accounts for the first half of the fascinating story of heavy ozone. With our work, the complete foundation is laid for numerous future applications of heavy ozone to atmospheric science, including the mesosphere and biosphere. Thanks Sincerely, Yuk Yung California Institute of Technology Pasadena, CA 91125 List of potential referees (in alphabetical order): Prof. Kristie A. Boering (boering@cchem.berkeley.edu) Department of Chemistry University of California, Berkeley Berkeley, CA 94720-1460 Tel: 510-642-3472 Dr. Charles H. Jackman (jackman@assess.gsfc.nasa.gov) NASA Goddard Space Flight Center Greenbelt, MD 20771 Tel: 301-614-6053 Prof. Konrad Mauersberger (Konrad.Mauersberger@mpi-hd.mpg.de) Division Atmospheric Physics Max-Planck-Institut für Kernphysik Heidelberg, Germany Tel: +49(0)6221-516-286 Dr. Thomas Röckmann (T.Roeckmann@mpi-hd.mpg.de) Atmospheric Isotope Physics Max-Planck-Institut für Kernphysik Heidelberg, Germany Tel: +49(0)6221-516-653 Dr. Michael E. Summers (msummers@physics.gmu.edu) Computational Sciences and Physics School of Computational Sciences George Mason University Fairfax, VA 22030-4444 Tel: 703-993-3971 Prof. Mark Thiemens (mthiemens@ucsd.edu) Department of Chemistry and Biochemistry University of California, Berkeley, San Diego La Jolla, CA 92093-0317 Tel: 858-534-6732 Prof. Ray Weiss (rfweiss@ucsd.edu) Scripps Institution of Oceanography University of California, Berkeley, San Diego La Jolla CA, 92093-0244 Tel: 858-534-2598