Electronic Spectrum and Photodissociation of ClONO in Comparison to BrONO

Abstract

A theoretical study of the low-lying singlet and triplet states of ClONO is presented. Calculations of excitation energies and oscillator strengths are reported using multireference configuration interaction, MRD-CI, methods with the cc-pVDZ + sp basis set. The calculations predict the dominant transition, 4(1)A' <-- 1(1)A', at 5.70 eV. The transition 2(1)A' <-- 1(1)A', at 4.44 eV, with much lower intensity nicely matches the experimental absorption maximum observed around 290 nm (4.27 eV). The potential energy curves for both states are found to be highly repulsive along the Cl-O coordinate implying that direct and fast dissociation to the Cl + NO2 products will occur. Photodissociation along the N-O coordinate is less likely because of barriers on the order of 0.3 eV for low-lying excited states. A comparison between the calculated electronic energies related to the two dominant excited states of ClONO and BrONO indicates that the transitions lie about 0.6 eV higher if bromine is replaced by chlorine. The stratospheric chemistry implications of ClONO and BrONO are discussed.

Ab Initio Characterization of ClNO3 Isomers

“…29 We used the cc-pVDZ basis set of double-ζ quality 30,31 with an additional s-Rydberg function located at the nitrogen center (R s (N) ) 0.028) and a negative ion p-function for the chlorine atom (R p (Cl) ) 0.049). From our present calculations on ClNO 2 32 and previous studies, 33 it is known that the changes in the excitation energies and transition probabilities between the results obtained with basis sets of double and triple-ζ quality are small; therefore, we believe that our calculated excitation energies have an error well below 0.3 eV. A summation threshold of 0.85 was used, which means that the sum of the squared coefficients of all reference configurations selected for each state is above 0.85.…”

An ab initio investigation of the ground and low-lying singlet and triplet electronic states of XNO2 and XONO (X = Cl, Br, and I)

“…ω 4 (b 2 ) NO 2 asym-str. ω 5 (b 2 ) NO 2 rock ω 6 (b 1 ) op-bend 92 and cis-BrONO. 93 In each case, they utilized the MRD-CI method with basis sets up to cc-pVTZ with an additional diffuse s on N and p function on the halogen (cc-pVTZ+sp).…”