Normal-Valent ClO_nX Compounds for n = 2, 3 and X = Cl, H:  An MCSCF Investigation

Abstract

A series of normal-valent compounds of potential interest with respect to atmospheric chlorine chemistry have been investigated using MCSCF ab initio methods with a good basis set. Comparisons of total energies of the compounds of interest with those of the radical precursors for complete active space wave functions including the bonding and antibonding orbitals of the molecules and the open shell orbitals of the radicals indicate that HOOCl, HOOOCl, and ClOOOCl are stable. Similar results for the compounds HOOH, ClOOCl, and HOOOH, which have been the subject of experimental or previous, more comprehensive, theoretical investigations, are presented for comparison. The predictions of stability for HOOCl and HOOOCl are of particular interest. HOOCl, which is the logical intermediate in the forward and backward reactions between HO + ClO and HOO + Cl, may be stabilized under some atmospheric and laboratory conditions. The role of HOOCl as an intermediate and the fact that the HOOCl adduct might be stabilized in certain parts of the stratosphere were suggested previously by Weissman et al. Also, Stimpfle et al. discussed HOOOCl as a possible intermediate in the HOO + ClO reaction but concluded on the basis of Benson's group additivity rules that its dissociation energy was probably too small for the molecule to be stable. The present results indicate that HOOOCl is sufficiently stable to be formed under some stratospheric conditions. At the MCSCF level of theory, HOOCl is predicted to have an electronic binding energy intermediate between those of ClOOCl and HOOH, while HOOOCl and ClOOOCl are predicted to have binding energies similar to that of ClOOCl.

Ab initio studies of ClOx reactions. VII. Isomers of Cl2O3 and their roles in the ClO+OClO reaction

“…There are no experimental parameters available for these two molecules. 20 Other previous calculations did not report this structure. 25͒ and ClOOOH ͑Ref.…”

Theoretical Investigation of Halogen-Oxygen Bonding and Its Implications in Halogen Chemistry and Reactivity

“…These complexes compete in stability with the peroxide normal valent forms YOOOCl, YOOOBr, and their classification is very sensitive to the method applied. At the CCSD(T)/6-311G(d,p), QCISD(T)/6-311G(d,p) levels of theory [42, 43], they are placed only ∼1-2 kcal/mol above the normal valent peroxide structures, while at the G2MP2 level they are found to be even more stable by ∼2-3 kcal/mol [19, 34, 43]. The corresponding I containing isomer, the iodic acid HOIO 2 , presents particular stability and it is far more stable than the normal valent peroxide isomer HOOOI, as we will see in the next paragraph.…”

“… (a) Reference [46], (b) reference [23], (c) reference [24], (d) reference [19], (e) reference [43], (f) reference [43] at the G2MP2 and the CCSD(T), QCISD(T) levels, respectively, (g) reference [27], (h) reference [34], (i) reference [42], (j) reference [49], (k) reference [53]. …”

Gas Phase Structures of Peroxides: Experiments and Computational Problems

“…Scheme 3).The OÀO bond lengths and dihedral angles in these peroxides are similar: 1.419(9) ,84(2)8 in FC(O)O-OC(O)F,[69] 1.426(10) , 87(3)8 in CF 3 C(O)O-OC(O)CF 3 [70] and 1.403(19) , 87(2)8 in CF 3 OC(O)O-OC(O)OCF 3 [71]. Surprisingly, the CO-OC dihedral angles in peroxides with two sp 2 hybridized substituents C(O)X are smaller than 908.…”

“…Most computational methods predict the bond angle and dihedral angle close to the experimental values, but fail in reproducing the OÀO and OÀCl bond lengths. [82][83][84][85][86][87][88][89][90][91][92][93][94] The HF method with large basis sets predicts the OÀO bond too short by 0.07 and the OÀCl bond too long by 0.05 . [85] The best agreement with the experimental bond lengths is obtained with the MP2 method and large basis sets.…”