| 1. |
- Palmer, Michael H., et al.
(författare)
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Combined theoretical and experimental study of the valence, Rydberg, and ionic states of chlorobenzene
- 2016
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 144:12
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Tidskriftsartikel (refereegranskat)abstract
- New photoelectron (PE) and ultra violet (UV) and vacuum UV (VUV) spectra have been obtained for chlorobenzene by synchrotron study with higher sensitivity and resolution than previous work and are subjected to detailed analysis. In addition, we report on the mass-resolved (2 + 1) resonance enhanced multiphoton ionization (REMPI) spectra of a jet-cooled sample. Both the VUV and REMPI spectra have enabled identification of a considerable number of Rydberg states for the first time. The use of ab initio calculations, which include both multi-reference multi-root doubles and singles configuration interaction (MRD-CI) and time dependent density functional theoretical (TDDFT) methods, has led to major advances in interpretation of the vibrational structure of the ionic and electronically excited states. Franck-Condon (FC) analyses of the PE spectra, including both hot and cold bands, indicate much more complex envelopes than previously thought. The sequence of ionic states can be best interpreted by our multi-configuration self-consistent field computations and also by comparison of the calculated vibrational structure of the B and C ionic states with experiment; these conclusions suggest that the leading sequence is the same as that of iodobenzene and bromobenzene, namely: (XB1)-B-2(3b(1)(-1)) < A(2)A(2)(1a(2)(-1)) < (BB2)-B-2(6b(2)(-1)) < (CB1)-B-2(2b(1)(-1)). The absorption onset near 4.6 eV has been investigated using MRD-CI and TDDFT calculations; the principal component of this band is B-1(2) and an interpretation based on the superposition of FC and Herzberg-Teller contributions has been performed. The other low-lying absorption band near 5.8 eV is dominated by a (1)A(1) state, but an underlying weak B-1(1) state (pi sigma*) is also found. The strongest band in the VUV spectrum near 6.7 eV is poorly resolved and is analyzed in terms of two pi pi* states of (1)A(1) (higher oscillator strength) and B-1(2) (lower oscillator strength) symmetries, respectively. The calculated vertical excitation energies of these two states are critically dependent upon the presence of Rydberg functions in the basis set, since both manifolds are strongly perturbed by the Rydberg states in this energy range. A number of equilibrium structures of the ionic and singlet excited states show that the molecular structure is less subject to variation than corresponding studies for iodobenzene and bromobenzene.
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| 2. |
- Palmer, Michael H., et al.
(författare)
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Combined theoretical and experimental study of the valence, Rydberg and ionic states of fluorobenzene
- 2016
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 144:20
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Tidskriftsartikel (refereegranskat)abstract
- New photoelectron spectra (PES) and ultra violet (UV) and vacuum UV (VUV) absorption spectra of fluorobenzene recorded at higher resolution than previously, have been combined with mass-resolved (2 + 1) and (3 + 1) resonance enhanced multiphoton ionization (REMPI) spectra; this has led to the identification of numerous Rydberg states. The PES have been compared with earlier mass-analyzed threshold ionization and photoinduced Rydberg ionization (PIRI) spectra to give an overall picture of the ionic state sequence. The analysis of these spectra using both equations of motion with coupled cluster singles and doubles (EOM-CCSD) configuration interaction and time dependent density functional theory (TDDFT) calculations have been combined with vibrational analysis of both the hot and cold bands of the spectra, in considerable detail. The results extend several earlier studies on the vibronic coupling leading to conical intersections between the (XB1)-B-2 and A(2)A(2) states, and a further trio (B, C, and D) of states. The conical intersection of the X and A states has been explicitly identified, and its structure and energetics evaluated. The energy sequence of the last group is only acceptable to the present study if given as (BB2)-B-2 < (CB1)-B-2 < D(2)A(1), a conclusion which is in agreement with most previous EOM-CCSD and other calculations. However, this symmetry ordering of the B and C states forces reconsideration of the nature of the PIRI spectrum. The coupling between these two states is induced by the a(2) modes, v(12) and v(14) and we propose that the 14(1) band is observed in the (BB2)-B-2 band in the PES for the first time, because of the improved resolution. This same assignment is given to the lowest energy band in the PIRI spectrum which was previously assigned as the origin band and further conclude that the entire PIRI spectrum is induced by v(12) and v(14). The relative intensities of the various Rydberg state peaks in the VUV absorption and REMPI spectra of fluorobenzene are very similar to those observed in the equivalent spectra of benzene. Published by AIP Publishing.
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| 3. |
- Palmer, Michael H., et al.
(författare)
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Interpretation of the photoelectron, ultraviolet, and vacuum ultraviolet photoabsorption spectra of bromobenzene by ab initio configuration interaction and DFT computations
- 2015
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 143:16
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Tidskriftsartikel (refereegranskat)abstract
- New photoelectron, ultraviolet (UV), and vacuum UV (VUV) spectra have been obtained for bromobenzene by synchrotron study with higher sensitivity and resolution than previous work. This, together with use of ab initio calculations with both configuration interaction and time dependent density functional theoretical methods, has led to major advances in interpretation. The VUV spectrum has led to identification of a considerable number of Rydberg states for the first time. The Franck-Condon (FC) analyses including both hot and cold bands lead to identification of the vibrational structure of both ionic and electronically excited states including two Rydberg states. The UV onset has been interpreted in some detail, and an interpretation based on the super-position of FC and Herzberg-Teller contributions has been performed. In a similar way, the 6 eV absorption band which is poorly resolved is analysed in terms of the presence of two pi pi* states of (1)A(1) (higher oscillator strength) and B-1(2) (lower oscillator strength) symmetries, respectively. The detailed analysis of the vibrational structure of the 2(2)B(1) ionic state is particularly challenging, and the best interpretation is based on equation-of-motion-coupled cluster with singles and doubles computations. A number of equilibrium structures of the ionic and singlet excited states show that the molecular structure is less subject to variation than corresponding studies for iodobenzene. The equilibrium structures of the 3b(1)3s and 6b(2)3s (valence shell numbering) Rydberg states have been obtained and compared with the corresponding ionic limit structures.
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