ACS Style uses CASSI abbreviations for journal titles when making references. A list of many journal abbreviations can be found in Appendix 14.1 (328-339). Abbreviations, full journal titles, and CODEN can also be found in the CAplus Core Journal Coverage List.
Online Guides to Using ACS Style
Chapter 14 References : Online copy of Chapter 14 from the ACS Style Guide (American Chemical Society)
ACS Style Guide (University of Wisconsin Madison)