1. a Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts , 02139 , USA
2. b Department of Chemistry , Emory University , Atlanta , GA , 30322 , USA
3. c Institute for High Temperatures of the Russian Academy of Sciences , Izhorskaya 13/19, Moscow , 127412 , Russia
4. d Harvard-Smithsonian Center for Astrophysics , 60 Garden Street, Cambridge , MA , 02138 , USA