Vibrational structure and vibronic coupling in the carbon 1s photoelectron spectra of benzene and deuterobenzene

Abstract

Vibrationally resolved C1s photoelectron spectra of benzene and d 6 -benzene have been recorded using monochromated synchrotron radiation at photon energies of 330 eV. The spectrum of normal benzene displays considerable vibrational structure. Particularly noteworthy is the strong excitation of a combined CCH-bending and CC-stretching mode which splits the main peak into two well-defined maxima. In d 6 -benzene, the vibrational energy levels are less well separated and the vibrational structure is reduced to strong asymmetry of the main peak and a broad tail extending toward higher ionization energy. The recorded spectra are analyzed using first-principle and curve-fitting procedures. A theoretical model that allows for incomplete localization of the core hole, results in very good fits to the experimental spectra of both benzene and d 6 -benzene.

Table-Top X-ray Spectroscopy of Benzene Radical Cation

“…The spectrum of neutral benzene (Bz) presented in panel 1(a) is taken with a flow of benzene molecules by referencing the high harmonic x-ray flux with no sample in the cell, as previously described 15 ; the spectrum matches well with previously reported results, 34,35,36,37,38,39 and it consists of four main peaks (labeled as A-D) below the 1sC core level ionization energy (290.37 eV). 40,41 The first peak at 285.2 eV, labeled as A, is the most intense feature and is known as the transition from the 1sC orbital to the π*(e2u) LUMOs, 42 as can be seen in the energy diagram in Fig 1(c). Peaks B, C and D are due to core-to-Rydberg transitions, as also discussed in detail in the companion theoretical paper, 29 which corrects a previously debated assignment of peak D as a transition to a higher π*(b1g) orbital, 35,38,39,43 to the new assignment of doubly degenerate transitions to Ry(s) and Ry(p) character.…”

Table-Top X-ray Spectroscopy of Benzene Radical Cation

“…(e) X-ray flux (purple line), see SI for details The spectrum of neutral benzene (Bz) presented in Figure 1(a) is taken with a flow of benzene molecules by referencing the high harmonic x-ray flux with no sample in the cell, as previously described 15 ; the spectrum matches well with previously reported results, 34,35,36,37,38,39 and it consists of four main peaks (labeled as A-D) below the 1sC core level ionization energy (290.37 eV). 40,41 The first peak at 285.2 eV, labeled as A, is the most intense feature and is known as the transition from the 1sC orbital to the π*(e2u) LU-MOs, 42 as can be seen in the energy diagram in Figure 1(c). Peaks B, C and D are due to core-to-Rydberg transitions, as also discussed in detail in the companion theoretical paper, 29 which corrects a previously debated assignment of peak D as a transition to a higher π*(b1g) orbital, 35,38,39,43 to the new assignment of doubly degenerate transitions to Ry(s) and Ry(p) character.…”

Table-Top X-ray Spectroscopy of Benzene Radical Cation

“…(e) X-ray flux (purple line), see SI for details The spectrum of neutral benzene (Bz) presented in Figure 1(a) is taken with a flow of benzene molecules by referencing the high harmonic x-ray flux with no sample in the cell, as previously described 15 ; the spectrum matches well with previously reported results, 34,35,36,37,38,39 and it consists of four main peaks (labeled as A-D) below the 1sC core level ionization energy (290.37 eV). 40,41 The first peak at 285.2 eV, labeled as A, is the most intense feature and is known as the transition from the 1sC orbital to the π*(e2u) LU-MOs, 42 as can be seen in the energy diagram in Figure 1(c). Peaks B, C and D are due to core-to-Rydberg transitions, as also discussed in detail in the companion theoretical paper, 29 which corrects a previously debated assignment of peak D as a transition to a higher π*(b1g) orbital, 35,38,39,43 to the new assignment of doubly degenerate transitions to Ry(s) and Ry(p) character.…”