Journal of Physical Chemistry A vol:109 issue:43 pages:9786-9794
In this work, the C2F4(X(1)A(g)) + O(P-3) reaction was investigated experimentally using molecular beam-threshold ionization mass spectrometry (MB-TIMS). The major primary products were observed to be CF2O (+ CF2) and CF3 (+ CFO), with measured approximate yields of 84(-11)(+7)% versus 16(-7)(+11)%, respectively, neglecting minor products. Furthermore, the lowest-lying triplet and singlet potential energy surfaces for this reaction were constructed theoretically using B3LYP, G2M(UCC, MP2), CBS-QB3, and G3 methods in combination with various basis sets such as 6-31G(d), 6-311+G(3df), and cc-pVDZ. The primary product distribution for the multiwell multichannel reaction was then determined by RRKM statistical rate theory and weak-collision master equation analysis. It was found that the observed production of CF3 (+ CFO) can only occur on the singlet surface, in parallel with formation of ca. 5 times more CF2O(X) + CF2(X(1)A(1)). This requires fast intersystem crossing (ISC) from the triplet to the singlet surface at a rate of ca. 4 x 10(12) s(-1). The theoretical calculations combined with the experimental results thus indicate that the yield of triplet CF2((a) over tilde B-3(1),) + CF2O formed on the triplet surface prior to ISC is <= 35%, whereas singlet CF2(X(1)A(1)) + CF2O is produced with yield >= 60%, after ISC. In addition, the thermal rate coefficients k(O + C2F4) in the T = 150-1500 K range were computed using multistate transition state theory and can be expressed as k(T) = 1.67 x 10(-16) x T-1.48 cm(3) molecule(-1) s(-1); they are in agreement with the available experimental results in the T = 298-500 K range.