1,721,217 research outputs found
Studies of some gas-phase oxidation reactions using electron spectroscopy and the electronic structure of some small molecules
No full textMost of this thesis is concerned with recording electron spectra arising either from photoionisation of gas-phase neutral molecules or from gas-phase chemi-ionisation reactions. The experimental techniques used, especially those involved with the use of high temperature evaporations are detailed in the early part of the thesis. Ab initio molecular orbital calculations were used in the interpretation of some of the photoelectron spectra.Chemi-ionisation reactions arising from the gas-phase oxidation of acetylene have been studied in some detail by recording chcmielcctron spectra for this reaction under a range of experimental conditions. The interpretation of the spectra was based largely on thermodynamic data and comparison with the results of previous work. Some general comments on the relevance of these studies to flame chemistry arc made.Studies of chemi-ionisation reactions which occur in the gas-phase oxidation of some lanthanide metals have also been performed using chemi-electron spectroscopy and chcmi-ion mass spectromctry. The use of approximate kinetic modelling of the reaction scheme, together with the experimental electron spectroscopic and mass spectrometric data, allowed information on the reactions to be obtained. The electron and ion spectra obtained were rationalised in terms of available thermodynamic data.The production of alkali metal monoxides (NaO and KO) in the gas-phase by use of the reaction between an alkali metal vapour and the oxidants Os or N2O allowed the low energy region of the UVPES of these metal oxides to be recorded. Assignment of the observed bands was achieved by the use of ab initio molecular orbital calculations. For M = Na and K, a band was seen from the M plus Os reaction that was not seen in the M plus N2O reaction. This band was assigned to the first ionisation of MO2 (M= Na, K). Preliminary spectra of LiO formed from the reaction of Li with N2O are also reported.Ab inilio calculations of the equilibrium geometries and vibrational frequencies of the alkaline earth dihalides BeF2, MgF2 and CaF2 have been performed.The effect of basis set superposition error (BSSE) on the calculated equilibrium bond angle in CaF2 has been studied, and the effects of BSSE on the calculated dissociation energies of the alkali monoxides NaO and KO have also been investigated.</p
The heaviest group 2 dihalide: RaAt2
No full textHigh level ab initio calculations, up to (R)CCSD(T) as well as B3LYP have been performed on, radium diastatide, RaAt2, employing effective core potentials augmented with large, flexible valence basis sets. RaAt2 is found to have a bent equilibrium geometry, with a bond angle of similar to134.50, but a very low barrier to linearity. In addition, we performed calculations on the lowest cationic states, and calculate the first adiabatic ionization energy to be 7.41 eV, corresponding to a X(2)B(2) - X(1)A(1) process. We also calculate the energies of the lowest neutral states and find that RaAt2 is likely to absorb in the ultraviolet
Preliminary calculations on the Na-N-2 complex
No full textHigh-level, RCCSD(T), calculations are performed on the molecular complex formed between a Na(S-2) atom and a N-2(X(1)Sigma(g)(+)) 9 molecule, using large basis sets. The complex is found to have a linear global minimum, with a D, value of only 24 cm(-1). The zeropoint energy is estimated to be around 16 cm(-1), suggesting that this is a very floppy complex. In addition, a T-shaped saddle-point lies only 7.5 cm(-1) above the potential energy minimum
Heats of formation of NaOH and NaOH+: ionization energy of NaOH
No full textRCCSD(T) calculations combined with large basis sets are employed to obtain the heats of formation and dissociation energies of NaOH and NaOH+. Our best values are ?H(f)(NaOH,0 K) = -44 +/- 1 kcal mol(-1) and D-0 = 79 +/- 1 kcal mol(-1). The ground state of NaOH+ is a X(2)Pi state, which is split by a very small Renner-Teller interaction. We calculate AIE (NaOH) = 7.87 +/- 0.05 eV, ?H(f)(NaOH+,0 K) = 137 +/- 1 kcal mol(-1), and D-0 = 16 +/- 1 kcal mol(-1). The proton affinity of NaO(X(2)?) is derived as 250 +/- 1 kcal mol(-1). In addition, we conclude that, experimentally, the Vibrational frequencies of neither NaOH nor NaOH+ are known with any reliability
The ionization energy of KO2 ((X)over-tilde(2)A(2)) and dissociation energies of KO2 and KO2+
No full textRCCSD(T) calculations, with an effective core potential for the inner electrons of potassium, and large polarized valence basis sets, have been used to calculate ionization energies of KO2. In addition, the binding energies of the ground electronic states of KO2, (X)over-tilde(2)A(2), and KO2+, X(3)Sigma(-), have been determined. Comparison with previous values is made, where possible, and an estimate made of the errors in our calculations. The binding energy of KO2+ is found to be very limited. It is concluded that the rôle of KO2+ in the upper atmosphere will be small
Heats of formation of LiOH(X1?+) and LiOH+(X2?): the ionization energy of LiOH
No full textRCCSD(T) calculations combined with large basis sets are employed to obtain the heats of formation of LiOH and LiOH+; in addition, the first adiabatic and vertical ionization energies of LiOH are obtained. Our best values are: ?H(f)(LiOH, 0 K) = -57.0+/--0.5 kcalmol(-1) and D-0 = 104+/-1 kcalmol(-1). The ground state of LiOH+ is a quasi-linear Renner-Tefler X2? state and AIE(LiOH) = 8.91+/-0.03 eV. ?H(f)(LiOH+, 0 K) = 148+/-2 kcalmol(-1) and D-0 = 23+/-1 kcalmol(-1). The proton affinity of LiO(X2?) is derived as 230+/-1 kcalmol(-1)
Spectroscopy and thermodynamics of LiS/NaS (X²? and A²?+) and LiS+/NaS+(X³?¯and A³?)
No full textPotential energy curves are calculated for the X(2)Pi and A(2)Sigma(+), states of LiS and NaS and the X(3)Sigma(-) and A(3)Pi states of LiS+ and NaS+. The RCCSD(T)/aug-cc-pVXZ levels of theory are employed (X = Q, 5 and infinity), where the infinityZ results are obtained at each bond distance, R, employing a two-point extrapolation to the basis set limit. From the three sets of curves, spectroscopic constants, ionization and dissociation energies are derived. Comparison is made to available experimental and calculational results
Ground electronic states of RbO2+, CsO2+ and FrO2: The ionization energies of RbO2 and CsO2
No full textCalculations are performed to establish the ground electronic states of RbO2+, CsO2+, and FrO2. In the case of the cations, both linear and C-2 nu orientations were considered; for FrO2, the two lowest electronic states, (2)A(2) and B-2(2), were considered in C-2 nu symmetry. In addition, calculations were also performed on the (X) over tilde (2)A(2) ground states of RbO2 and CsO2 to derive ionization energies. Binding energies and heats of formation are also derived. The bonding in FrO2 is found to be less ionic than that of RbO2 and CsO2
Spectroscopy and thermodynamics of KO+
No full textHigh-level RCCSD(T) calculations are employed to generate potential energy curves for the (3)Sigma(-) and (3)Pi states of KO+. First, these curves are employed to obtain spectroscopic constants for the two cationic states. Second, the curves are employed together with our previous results on KO, to obtain accurate ionization energies for the KO+ - KO processes, for the states involved. We conclude that the first adiabatic ionization energy of KO is 6.98 +/- 0.05 eV, with D-0(KO+) = 1460 +/- 20 cm(-1)
Thermochemistry of HgCH<sub>3</sub> and HgCH<sub>3</sub><sup>+</sup> and the ionization energy of HgCH<sub>3</sub>
No full textHigh-level ab initio calculations are performed on HgCH3 and HgCH3+. For HgCH3+, the obtained geometry and vibrational frequencies could be compared to Raman studies of HgCH3+ interacting with biomolecules. HgCH3 was found to be a weakly bound species with a binding energy, D0, of only 3 kcal mol-1. The first adiabatic ionization energy was calculated to be 7.3 ± 0.1 eV, corresponding to an (a1)-1 ionization. The heats of formation were deduced for both the neutral and cation at 298 K, giving values of ΔHf = 45 ± 2 and 235 ± 2 kcal mol-1, respectively
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