Quantum state-to-state vacuum ultraviolet photodissociation dynamics of small molecules

Abstract

The present review focused on selected, recent experimental progress of photodissociation dynamics of small molecules covering the vacuum ultraviolet (VUV) range from 6 eV to 20 eV. These advancements come about due to the available laser based VUV light sources, along with the developments of advanced experimental techniques, including the velocitymap imaging (VMI), H-atom Rydberg tagging time-of-flight (HRTOF) techniques, as well as the two-color tunable VUV-VUV laser pump-probe detection method. The applications of these experimental techniques have allowed VUV photodissociation studies of many diatomic and triatomic molecules to quantum state-to-state in detail. To highlight the recent accomplishments, we have summarized the results on several important molecular species, including H 2 (D 2 , HD), CO, N 2 , NO, O 2 , H 2 O (D 2 O, HOD), CO 2 , and N 2 O. The detailed VUV photodissociation studies of these molecules are of astrochemical and atmospheric relevance. Since molecular photodissociation initiated by VUV excitation is complex and is often governed by multiple electronic potential energy surfaces, the unraveling of the complex dissociation dynamics requires state-to-state cross section measurements. The newly constructed Dalian Coherent Light Source (DCLS), which is capable of generating coherent VUV radiation with unprecedented brightness in the range of 50−150 nm, promises to propel the photodissociation experiment to the next level.

Forbidden atomic carbon, nitrogen, and oxygen emission lines in the water-poor comet C/2016 R2 (Pan-STARRS)

“…[OI] G/R emission ratio. There are several recent experimental developments in detecting O( 1 D) via the photodissociation of CO 2 (Sutradhar et al 2017;Lu et al 2015;Song et al 2014;Schmidt et al 2013;Gao & Ng 2019;Pan et al 2011). But these measurements are limited to a small energy range (<1 eV) and do not provide the O( 1 D) yield over a wide wavelength range (from dissociation threshold to 1000 Å) which is essential to determine the average dissociation ratio of O( 1 S)/O( 1 D) in the photodissociation of CO 2 .…”

Strong and selective isotope effect in the vacuum ultraviolet photodissociation branching ratios of carbon monoxide

“…N( 2 D) can be much more efficiently trapped due to its higher reaction rates with H 2 compared with O( 3 P), and this caused the much higher degree of depletion for 15 N compared with 17 O and 18 O in the Sun as observed by the Genesis mission. To verify this assumption, the photodissociation branching ratios of 12 C 16 O have been measured recently 28–33 , which showed that photodissociation of 12 C 16 O not only generates C and O atoms in the ground state, but also produces significant amount of C and O atoms in the excited states, and the ratios between them strongly depend on the specific rovibronic state of 12 C 16 O being excited. These observations clearly showed that the initial assumption by Clayton is oversimplified.…”

A New Band System of the Dicarbon Molecule in the Vacuum Ultraviolet Region

“…Other than the two electronic states described above accessed in the UV region, our knowledge of the photoabsorption and photodissociation properties of C 2 in the vacuum ultraviolet (VUV) region between the lowest dissociation and ionization thresholds is still largely blank, as shown in Figure . Short-wavelength VUV radiation is ubiquitous in the universe, and the photodissociation of small molecules in the VUV region plays an important role in astrochemistry and planetary atmospheric chemistry. − …”