ELSEVIER Journal of Molecular Structure (Theochem) 310 (1994) 13-1 6 THEO CHEM Determination of the heat of formation of oxygen containing radicals using density functional theory E. Sicilia", F.P. Di Maio" , N. RUSSO*,b "Centro Processi a Membrana e Reattori Chimici-CNR , 1-87030 Arcavacata di Rende (CS ), Italy "Dipartimento di Chimica , Universita' della Calabria, 1-87030 Arcavacata di Rende (C S), Italy (Received 19 July 1993; accepted 30 September 1993) Abstract The heat of fo rmat ion of the CH 302 rad ical wa s det ermin ed using the LC GTO-NLSD method . The goo d agreement with experiment obtained for the methylperoxy r adical and previ ously determin ed values for severa l oxygen co ntai ning rad icals indicates that the m eth od is able co rrectly to reproduce th e he at s of formati on and ca n be con sidered a promi sin g tool for the thermod ynamic study of orga nic systems. 1. Introduction The important role that a knowledge of the heat of formation (LlH?) of chemical systems plays in both basic and applied sciences is well known. In many cases, very accurate enthalpies of formation have been obtained experimentally. However, experi- mental techniques are generally less successful for transient species such as free radicals. For example, the heat of formation of the hydroperoxyl radical (H0 2 ) has been measured using many different methods since 1955. The experimental values that are available range from -6.9 to 4.6kcalmol- 1 [I]. Although modern experimental techniques have improved the reliability of results, there are still systems that can be considered "difficult" to study [2]. In these cases reliable theoretical determinations are very useful for obtaining information and sup- porting experimental results. Previously [3,4] we have successfully calculated the heat of formation *Corresponding author. of some radicals by using the LCGTO -NLSD method. In this paper , we report our det ermina- tion of the LlH? of CH 302 , and summarize the results we have obtained previously for oxygen cont aining radicals that play an important role in a variety of chemical processes of relevance to atmospheric and combustion chemistry. 2. Method and computational details The computations were performed using the linear combination of gaussian type orbitals- local spin den sity (LCGTO-LSD ) method which was originally proposed by Sambe and Felton [5] and has been largely developed and extended in the last few years [6,7]. In the case of the non-local approach (LCGTO-NLSD) , the total energy is obtained by E NLSD = E LSD + Ex + E c The non-local terms (Ex and E c ) were calculated using the density gradient and employing the 0166-1280/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI0166-1280 (93 )0351 8- C