Exploring the vacuum ultraviolet photochemistry of astrochemically important triatomic molecules

The recently constructed vacuum ultraviolet (VUV) free electron laser (FEL) at the Dalian Coherent Light Source (DCLS) is yielding a wealth of new and exquisitely detailed information about the photofragmentation dynamics of many small gas-phase molecules. This Review focuses particular attention on five triatomic molecules-H2O, H2S, CO2, OCS and CS2. Each shows excitation wavelength-dependent dissociation dynamics, yielding photofragments that populate a range of electronic and (in the case of diatomic fragments) vibrational and rotational quantum states, which can be characterized by different translational spectroscopy methods. The photodissociation of an isolated molecule from a well-defined initial quantum state provides a lens through which one can investigate how and why chemical reactions occur, and provides numerous opportunities for fruitful, synergistic collaborations with high-level ab initio quantum chemists. The chosen molecules, their photofragments and the subsequent chemical reaction networks to which they can contribute are all crucial in planetary atmospheres and in interstellar and circumstellar environments. The aims of this Review are 3-fold: to highlight new photochemical insights enabled by the VUV-FEL at the DCLS, notably the recently recognized central atom elimination process that is shown to contribute in all of these triatomic molecules; to highlight some of the potential implications of this rich photochemistry to our understanding of interstellar chemistry and molecular evolution within the universe; and to highlight other and future research directions in areas related to chemical reaction dynamics and astrochemistry that will be enabled by increased access to VUV-FEL sources. This review summarizes rich photochemistry of triatomic molecules in the vacuum ultraviolet region, and their potential implications to our understanding of interstellar chemistry and molecular evolution in the universe.

Automated summary

This review highlights the rich photochemistry of triatomic molecules in the vacuum ultraviolet region and discusses their potential implications for our understanding of interstellar chemistry and molecular evolution in the universe. The study focuses on the photofragmentation dynamics of five triatomic molecules-H2O, H2S, CO2, OCS, and CS2-using the recently constructed VUV free electron laser. The review aims to provide new photochemical insights, explore the implications of this photochemistry for interstellar chemistry, and identify future research directions in chemical reaction dynamics and astrochemistry enabled by VUV-FEL sources.