The development of in situ photon-in/photon-out soft X-ray spectroscopy on beamline 7.0.1 at the ALS

Highlights: ► Development of various cells for in-situ electronic structure study. ► Gas cell for study of gas molecules and catalytic reactions. ► Liquid cell for study of molecular liquids and ion salvation. ► In-situ cell for study of electrochemical reactions. -- Abstract: This is a mini-review about the development of various cells built over the years for in situ electronic structure study of gas molecules, molecular liquids, gas/solid and liquid/solid interfaces. In the study of gas molecules, the role of the parity selection rule in the case of homonuclear diatomic molecules (N2 and O2) is revealed and illustrated by the resonant X-ray emission spectra, while the occurrence of forbidden transitions in CO2 is explained in terms of dynamical symmetry breaking due to vibronic coupling. X-ray emission spectroscopy has been used to elucidate the molecular structure of liquid water, liquid methanol, methanol–water mixtures, as well as cation–water solutions, and to reveal the influence of the intermolecular interaction on the local electronic structure of water molecules. The in situ soft X-ray spectroscopy experimental studies of electrochemical reactions were also performed under ambient conditions