Electronic structure of triatomic interhalogens

Abstract

Although a number of trihalide ions have long been experimentally characterized [I], very little is known about the parent neutral radicals. Available experimental [ 11 and ab initio theoretical [2,3] Ungemach and Schaefer [2] support the experimental structure of ClF2, but no such theoretical study has yet been made to substantiate the observed structure of c13. The CND0/2 (spd) calculations of Vasini and Castro [9] on C I S and CI3 indicate that both the radicals possess a linear symmetric structure. In view of the fact that they obtained very irregular angular potential (AP) curves (the AP curve of C I S shows a minimum at 100' and constant energy in the range of 17Oo-18O0, whereas the AP curve of C13 shows minima at looo, 160°, and 180') and performed the SCF iterations on C13 with a precision of hartree, their conclusion is very much questionable. Deb et al.[ID] also performed CND0/2 (spd) calculations on CIF2 and predicted a linear symmetric structure. It is, however, well known [l 11 that CND0/2 (spd) calculations with original parameters [12] overestimate the bond angles and underestimate the bond lengths. We therefore carried out CND0/2 and INDO calculations [13] on CIF2 and c 1 3 using sp basis set, and observed that both of them possess symmetric bent structure. In order to obtain more information about the structural pattern of triatomic interhalogens in general, we have performed similar calculations on four additional systems, namely, F3, FFCl (the asymmetric conformer of CIFz), ClFCl (the symmetric conformer of CIzF), and ClClF (the asymmetric conformer of C12F). Since it is not convenient to discuss molecular electronic structure on the basis of composition and population of the occupied MO' s obtained from UHF-type calculations, we have also performed RHF-type calculations on some of the molecule.For the UHF calculations we have followed the same method of calculations as outlined in our previous paper [I 31. The RHF The calculated ground state geometry of F3, FCIF, FFCI, CIFCI, CICIF, and CI3 is given in Table I along with the available experimental and ab initio theoretical values. We carried out RHF calculations only for FCIF, ClFC1, and C13 since we thought that the results of these calculations might be considered as representative of the entire series. Considering the equilibrium geometrical parameters in Table I we find that with the exception of CIFCI, all the molecules are predicted to have a bent structure. The RHF calculations yield somewhat smaller interbond angles for the bent molecules than the corresponding UHF calculations. A similar trend isbbserved when the results of CND0/2 and INDO calculations are compared. As regards

Direct observation and reactions of Cl3 radical

“…[17][18][19][20][21][22][23] Emission spectra attributable to Cl 3 were observed by Kawasaki et al 14 and Wright et al 15 These data were in reasonable agreement with each other. An IR spectrum of Cl 3 in a Kr matrix was reported by Nelson and Pimentel.…”

Photolysis of Matrix-Isolated HCl−Cl2 Complexes: Electronic Absorption and Emission Spectra Provisionally Assigned to Cl3

“…Following this work, Wright et al suggested that a 370−420 nm emission band, observed when Cl 2 was photodissociated under relatively high-pressure conditions, might also originate from Cl 3 . In parallel with the experimental efforts there have been many attempts to calculate potential energy surfaces for trihalogens using ab-initio ,− and semiempirical methods. ,− …”

“…In parallel with the experimental efforts there have been many attempts to calculate potential energy surfaces for trihalogens using ab-initio 15,[24][25][26] and semiempirical methods. 9,[27][28][29][30][31][32] Recently, additional interest in the trihalogens has been generated by novel time-resolved studies of the Br + I 2 reaction. 1,[33][34][35][36] From the results on this system, it appears that trihalogens, accessed through photodissociation of HX-YZ complexes, may be especially suitable for real-time studies of reaction dynamics.…”

“…The hydrogen atom readily escapes the matrix cage, [37][38][39] while the halogen atoms remain trapped. [40][41][42] To test this method, we have examined Cl 3 as the search for the spectrum could be guided by theoretical calculations 15,[26][27][28][29][30][31][32] and the gas phase results. 14,15…”