Structure, bonding and reactions of no and no+ complexes

Mack, Paul (1999) Structure, bonding and reactions of no and no+ complexes. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

In this thesis, the structure and bonding of NO complexes have been studied using resonance enhanced multiphoton ionization (REMPI) spectroscopy and zero kinetic energy pulsed field ionization (ZEKE-PFI) spectroscopy. Spectroscopic studies of Rg·NO complexes (where Rg = Ar, Kr and Xe) and the N₂·NO complex are reported in Chapters 2-8. Some reactions of NO⁺ complexes have been studied using ab initio molecular orbital methods and these studies are presented in Chapter 9.

A structured spectrum for the one-photon Ã²Σ⁺ ← X̃;²II transition in Ar·NO has been recorded using one and two-colour REMPI spectroscopy. Simulations of the experimentally observed one-colour spectrum were performed using two different models appropriate for calculating the rovibrational levels of open-shell complexes; the simulations are described in Chapters 4 and 5. Information concerning the properties of the Ã²Σ⁺ of Ar·NO was obtained and it was possible to determine the vibrationally averaged structure of the Ã state complex in two different intermolecular stretching levels.

Structured ZEKE-PFI spectra were recorded with excitation via two different vibrational levels of the Ã²Σ⁺ state of Ar·NO; the spectra are presented and discussed in Chapter 6. Transitions to higher-lying vibrational levels of AR^.NO⁺were observed and the ZEKE-PFI spectra were interpreted using a simple model to describe the intermolecular vibrational modes of the Ar·NO⁺ complex. Additionally, the overall appearance of each ZEKE-PFI spectrum was discussed in relation to the different vibrationally averaged structures of Ar·NO⁺ and the Ã²Σ⁺ state of AR^.NO.

The one-photon Ã²Σ⁺ ← X̃;²Π transitions in Kr·NO and Xe·NO were studied using one and two-colour REMPI spectroscopy and structured spectra of these transitions are presented in Chapter 7. The dissociation energies of the X̃; and Ã states of these complexes were estimated and it was found that although the A²Σ⁺ state of NO is a Rydberg state, the Ã of Kr·NO and Xe·NO do not exhibit Rydberg behaviour. Spectra of the two-photon C̃;Π ← X̃;²Π transitions in Ar·NO, Kr·NO and Xe·NO were also recorded and simulations of these spectra are reported. Resonanace enhanced multiphoton excitation and ionization of Kr·NO and Xe·NO via the Ã²Σ⁺ state was found to generate Kr⁺ and Xe⁺ as well as Kr·NO⁺ and Xe·NO⁺; additionally the two-photon ionization of Xe·NO with excitation via the C̃;²Π state was found to yield only Xe⁺ and no Xe·NO⁺. The mechanism of the formation of rare ions in each case is discussed in Chapter 7.

One-colour REMPI spectroscopy was also used to study the one-photon Ã²Σ⁺ ← X̃;²Π transition N₂·NO. This work is described in Chapter 8. The information gained from studying the equivalent transition in Ar·NO was used to interpret the REMPI spectrum of N₂·NO recorded in this work, and a simulation of part of the spectrum allowed a determination of the structure of N₂·NO in particular intermolecular stretching level of the Ã state. Furthermore, dissociation energies of the X̃; and Ã states of the complex were estimated, and the properties of the Ã state of N₂·NO are compared with those of the corresponding states in the Rg·NO complexes (where Rg = AR, Kr and Xe).

Ab initio molecular orbital calculations have been performed on the atmospherically important complexes, N₂·NO⁺, CO₂·NO⁺ and H₂O·NO⁺, and the results are discussed in Chapter 9. Equilibrium structures of each complex were determined using a variety of basis sets at various levels of theory, and harmonic vibrational frequencies for the complexes at the equilibrium geometries were also computed. A simple statistical mechanical analysis using the ab initio results was utilized to calculate the thermochemical properties of the NO⁺ complexes; thermodynamic values for some ion-molecule reactions involving these complexes were then calculated. A single theoretical approach appropriate for treating each of the X·NO⁺ complexes (where X = N₂, CO₂ and H₂O) was developed, and in Chapter 9, the results of the calculations are disscussed in relation to the atmospheric chemistry of NO⁺ complexes.