Symmetry-Resolved Absorption Spectra of Vibrationally Excited ${\mathrm{CO}}_2$ Molecules

Symmetry-resolved x-ray absorption spectroscopy has been first carried out on high-temperature molecules. From the angle-resolved ion yield spectra of ${\mathrm{CO}}_2$ both at room temperature and at 430 °C, symmetry-resolved absorption profiles of the C $1s^{-1}2{\pi }_u$ and O $1s^{-1}2{\pi }_u$ resonances have been extracted for the vibrational ground state molecules and bending-vibration excited ones. The profiles change dramatically between them, and the Renner-Teller effect becomes more evident for the vibrationally excited molecules. The effects of the multimode vibronic coupling are suggested for the O $1s^{-1}2{\pi }_u$ and O $1s^{-1}3s{\sigma }_g$ resonances.

Figure 1

Absorption spectra in the ${\mathrm{CO}}_2$ C $1s^{-1}2{\pi }_u$ excitation region: (a) 0° spectra measured at room temperature and at 430 °C and the TIY spectra; (b) extracted ground and vibrationally excited state 0° spectra. (c),(d) 90° spectra with same descriptions as (a) and (b), respectively.

Figure 2

Absorption spectra in the ${\mathrm{CO}}_2$ O $1s^{-1}2{\pi }_u$ excitation region. See the caption of Fig. 1 for details.

Figure 3

Potential energy curves for the C $1s^{-1}2{\pi }_u$ $A_1$ and O $1s^{-1}2{\pi }_u$ $A_1$ states as functions of the O-C-O angle, calculated using the Hartree-Fock approximation within the equivalent core model. The curves are generated from the results given in Ref. 14.