The Collaborative International Dictionary of English v.0.48:

astrochemistry \astrochemistry\ n.
   the branch of science involving astronomy and chemistry which
   studies the chemical composition, chemical reactions, and
   evolution of matter in outer space. -- as`tro*chem"ic*al,
   a. -- as`tro*chem"ic*al*ly, adv.
   [PJC]