A Quantum chemical study on the potential energy surface of Mg 1 S N 2 O reaction Boggavarapu Kiran, Chris Vinckier, Minh Tho Nguyen * Department of Chemistry, University of Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium Received 23 April 2001; in ®nal form 21 June 2001 Abstract The singlet  1 A 0  potential energy surface PES) of the Mg  N 2 O reaction has been studied at both MP2/6-311+G  and CCSDT)/6-311+G  levels.Twokindsofreactionchannelshavebeenidenti®ed:the®rstoneiswhentheMgatom approaches N 2 OinaperpendicularfashionbMg±O±N  90:0°)andthesecondiswhenMgapproachesfromtheend- onoxygenside)ofN 2 ObMg±O±N  148:0°).TheCCSDT)activationbarrierfortheperpendicularapproachis48.8 kJ/mol and compares well with the experimentally determined value 44:3  1:3kJ=mol. The transition structure for the end-on approach has higher energy barrier, 95.7 kJ/mol. Charges analysis and electron density calculations by atoms-in-molecule theory showed that the reaction mechanism is controlled by covalent interactions between the Mg atom and the O end of N 2 O rather than by an electron transfer from the Mg atom to the N 2 O molecule. Ó 2001 Elsevier Science B.V. All rights reserved. 1. Introduction Reactions in the gas phase of metal atoms M) with nitrous oxide N 2 O have generated in the past considerable experimental and theoretical in- terest. Studies in ¯ames [1] and molecular beam experiments [2,3] have shown that due to the high exothermicity of these reactions, metal oxides MO) were formed at various levels of electronic excitation. In view of the eciency of these reac- tions, the addition of metals to combustion sys- tems has recently been considered as a possible way of reducing the emission of the greenhouse N 2 O gas [4]. Anexcellentreviewof the state of the art onthe kinetics of the alkali and alkaline earth atom re- actions with N 2 O was given by Plane [5]. Two in- teresting features of these reactions are worth mentioning here. First it was seen that the second- order rate constants of the Li, K, and Ca=N 2 O reactions were characterized by a non-Arrhenius behavior in the temperature range between 250 and1000Kandthiscouldbeexplainedreasonably well by assuming two reaction paths with su- ciently dierent Arrhenius parameters. Secondly, the Mg 1 S=N 2 O reaction showed a large activa- tion energy of 39:6  1kJ=mol [6] Mg 1 S N 2 O ! MgO  N 2 1 whichwascon®rmedinalaterstudywhereavalue of44:3  1:3kJ=molhasbeendetermined[7].This largeactivationenergystaysinsharpcontrastwith the value of 3:4  0:6kJ=mol derived for the www.elsevier.com/locate/cplett 17 August 2001 Chemical Physics Letters 344 2001) 213±220 * Corresponding author. Fax: +32-16-327992. E-mail address: minh.nguyen@chem.kuleuven.ac.be M.T. Nguyen). 0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0009-261401)00773-4