Symmetry-resolved soft x-ray absorption spectroscopy: its application to simple molecules

Abstract

This paper reviews our recent progress on the angle-resolved photoion-yield spectroscopic (ARPIS) technique applied to the K-shell excitations of the simple linear molecules, N2, CO, C2H2, O2, CO2, N2O, OCS and CS2. This spectroscopic technique enables us to distinguish symmetries of electronic states; e.g., the ΔΛ = 0 parallel and ΔΛ = ±1 perpendicular transitions for the diatomic molecules can be distinguishable. We call this technique symmetry-resolved inner-shell excitation spectroscopy. The complete symmetry resolution is rationalized by the axial-recoil fragmentation. Moreover, the angular distribution of fragment ions is directly related to the molecular orientation upon the photoabsorption and the vibrations; therefore, the ARPIS measurement can be used to reveal complicated vibronic couplings in polyatomic molecules in terms of anisotropy in fragmentation. We have studied Rydberg-valence mixings, vibronically induced 1s → Rydberg excited states, and strong bending-mode couplings in Renner–Teller split 1s →π* states for the linear molecules through the ARPIS spectra.

Symmetry and vibrationally resolved absorption spectra near theN Kedges ofN2O: Experiment and theory

“…1), which is also discernible in the TIY spectrum as a shoulder (see also Ref. [22]) but which is completely absent in the ARIY [I(90 • )] spectrum, has been identified previously as the N t 1s → 3sσ Rydberg state [10]. An additional spectral feature is readily visible at ∼404.23 eV, which might be due to the ν 3 excitation of the 3sσ (N t 1s −1 ) Rydberg state.…”

“…An additional spectral feature is readily visible at ∼404.23 eV, which might be due to the ν 3 excitation of the 3sσ (N t 1s −1 ) Rydberg state. Such an excitation may not be totally unexpected because the mixing of the Rydberg and valence states, as discussed previously [10], may result in distortion of the PES along the q 1 and/or q 3 normal coordinates. Furthermore, we also noticed that the peak width of the 3sσ excitation appeared to be broader than the nsσ (N t ) peaks, which might further support this interpretation.…”

“…1) in the TIY spectrum are the well-known N t 1s −1 π * and N c 1s −1 π * resonances, respectively [10,[12][13][14][15][16]21,22]. They are also present in the 0 • measurements where their maxima are shifted by ∼0.1 eV towards lower photon energy because of the Renner-Teller effect, as discussed in detail previously [10,16]. Note that the PES of the N t 1s −1 π * state is bound in the N-O coordinate as in the O 1s −1 π * excited states [23], whereas that of the N c 1s −1 π * state is repulsive in this coordinate as discussed further later in this paper.…”

“…), fragment ions are preferentially detected parallel to the direction of the electric field vector of the linear polarized light, whereas for absorption transitions of = ±1 (i.e., → , → , etc. ), fragment ions are detected preferentially perpendicular to the direction of the electric field vector [10]. This method is therefore * ehara@ims.ac.jp often referred to as "symmetry-resolved" x-ray absorption spectroscopy [10].…”

“…), fragment ions are detected preferentially perpendicular to the direction of the electric field vector [10]. This method is therefore * ehara@ims.ac.jp often referred to as "symmetry-resolved" x-ray absorption spectroscopy [10].…”