The electronic states of thiazole studied by VUV absorption spectroscopy and ab initio configuration interaction methods

Abstract

The thiazole VUV absorption spectrum over the range 5-12 eV shows intense bands near 5.4, 6.0, 7-7.8, 8.2-8.8, 9.2-10.1 and 10.2-11.0 eV; there is marked vibrational structure in the 7.5-8.5 and 10.2-11 eV regions. A number of Rydberg states have been identified, largely from IE 1 , but also tentative values for ones from IE 2 and IE 4 . Electronic excitation energies for valence and Rydberg-type states have been computed using ab initio multi-reference multi-root CI methods, and these have been compared with the VUV envelope. Calculated energies for low-lying Rydberg states are close to those expected, and there is generally a good correlation between the theoretical intensities and calculated density of states, with the experimental envelope. The CI studies used a triple zeta + polarization basis set, augmented by diffuse (Rydberg) orbitals. The lowest absorption bands are dominated by intense pp * (A 0 ) valence states, together with LP N p * and pr * states, which are relatively weak. The lowest Rydberg states arise from excitation of the occupied MOs in the sequential order p 4 < r 18 (LP N ) < p 3 < p 2 < r 17 (LP S ) this same order is determined by CI for ionisation in the UV-PES spectrum. Adiabatic structures of the r-and p-triplets, -cations and the p-anion have been compared with the ground state structure. The known phosphorescence of thiazole is from the 3 A triplet state (C 1 symmetry) where significant twisting of C 5 H and S to opposite sides of the mean plane occurs. Some theoretical molecular properties of thiazole are described, which give good agreement with microwave spectral data.

Isomeric effects on the electron impact scattering for selected five membered heterocyclic ring molecules

“…Therefore, the present study is an attempt to see how these observed variations in the target properties affect the electron impact scattering crosssectional data. Comparing our present results with the available data, it is observed that the calculated ground state energies align closely with the existing data [24][25][26][27]. Additionally, our calculated dipole moment demonstrates excellent agreement with the available experimental data [28] in comparison to those value reported by Kossoski & Bettega [23], notably in the case of isoxazole.…”

VUV photodissociation of thiazole molecule investigated by TOF-MS and photoelectron photoion coincidence spectroscopy

“…The highest occupied valence molecular orbitals of thiazole in the VUV, calculated at MP2(full)/aug‐cc‐pVTZ level, have the following energies (eV) and symmetries: 9.35 (A″), 10.75 (A″), 11.87 (A′), 13.89 (A′), 15.42 (A″), 15.58 (A′), 16.33 (A′), 19.10 (A′), 21.22 (A′). The order for the main valence orbitals and Rydberg states of thiazole molecule has been previously discussed by Palmer . Considering the Cs symmetry of this molecule, no complete separation of the valence and Rydberg orbitals may be observed, thus some mixing of the valence molecular orbitals is expected.…”

“…Despite the relevance of spectroscopic investigations concerning the electronic structure, photoionization and dissociation dynamics, as well as the study of resulting ionic fragments and radical species from the free thiazole molecule, only a limited number of reports have been found in the literature. Briefly, the valence absorption and photoelectron spectra of thiazole molecule have been reported by Daamen et al ., and Palmer . The latter reported the vertical ionizations energies in the VUV range and the assignments based on ab initio calculations.…”

Photoionization and ionic dissociation of the C3H3NS molecule induced by soft X‐ray near the C1s edge

“…Very few theoretical and experimental studies for thiazole dedicated to the valence electronic levels can be found in the literature . On the other hand, we noticed a lack of information concerning the processes of electronic excitation and relaxation dynamics, photoionization, and photodissociation, involving the core electron levels for this molecule.…”