1. Department of Chemistry, Rice University, Houston, TX 77005, USA
2. Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, GA 30322, USA
3. SETI Institute and NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035, USA
4. Departamento de Quimica, Universidade de Coimbra, 3004535 Coimbra, Portugal