The electronic states of isoxazole studied by VUV absorption, electron energy-loss spectroscopies and ab initio multi-reference configuration interaction calculations

Threshold photoelectron studies of isoxazole over the energy range 9.9–30eV

“…The uncertainty in the energies obtained from the fitting is estimated to be 30 meV. The table also gives the results of CI calculations [3] and the assignments of the bands. The broad feature between 13 eV and 16.5 eV is well fitted by five bands.…”

“…In the last work [15], photoelectron angular distributions were also measured and compared with the firstorder calculations. More recently Walker et al [3] presented the He(I) photoelectron spectra obtained with an improved resolution of 20 meV.…”

“…The effect of introducing the N atom into the furan ring results in a shortening of the 2-3 distance between the nitrogen and carbon atoms in the double bond and an increase in the C 3 bond angle [2,3]. These changes in the geometrical parameters affect the energies of the molecular orbitals, lower the vertical attachment energies (unoccupied orbitals) [2] and increase the ionization energies (occupied orbitals) in isoxazole as compared to furan [3]. Both isoxazole and furan have a fully conjugated set of π-electrons with the two highest occupied orbitals being π 2 and π 3 .…”

“…The vibrational modes and structural properties of the neutral isoxazole (and isoxazole-d 3 ) molecules have been determined from measurements of Raman and IR spectra in the vapour phase [6][7][8][9], aided by extensive theoretical calculations [8,[10][11][12]. In the most recent calculations [11,12], the IR and Raman spectra of isoxazole and isoxazole-d 3 have been reassigned with the aid of DFT theory [11] and a systematic study of the anharmonic vibrational frequencies has been carried out using both the B3LYP density functional and MP2 ab initio techniques [12]. The totally symmetric 1 (A')-13 (A') modes are the in-plane vibrations while the 14 (A")- 18 (A") are out-of plane vibrations.…”

“…The 15(a') 2 orbital is the nitrogen lone pair (LP N ) 2 and the 1a", 2a" and 3a" orbitals are labeled π 1 , π 2 and π 3 , respectively. Ionization energies of the orbitals of isoxazole have been calculated using the Hartree-Fock method [4,5] and more recently by the configuration interaction (CI) method with the inclusion of Green' s Function and Tamm-Dancoff non-diagonal approximations [3].…”