Airfoil sampling of a pulsed Laval beam with tunable vacuum ultraviolet synchrotron ionization quadrupole mass spectrometry: Application to low-temperature kinetics and product detection

Abstract

A new pulsed Laval nozzle apparatus with vacuum ultraviolet (VUV) synchrotron photoionization quadrupole mass spectrometry is constructed to study low-temperature radicalneutral chemical reactions of importance for modeling the atmosphere of Titan and the outer planets. A design for the sampling geometry of a pulsed Laval nozzle expansion has been developed that operates successfully for the determination of rate coefficients by time-resolved mass spectrometry. The new concept employs airfoil sampling of the collimated expansion with excellent sampling throughput. Time-resolved profiles of the high Mach number gas flow obtained by photoionization signals show that perturbation of the collimated expansion by the airfoil is negligible. The reaction of C 2 H with C 2 H 2 is studied at 70 K as a proof-of-principle result for both low-temperature rate coefficient measurements and product identification based on the photoionization spectrum of the reaction product versus VUV photon energy. This approach can be used to provide new insights into reaction mechanisms occurring at kinetic rates close to the collision-determined limit.3

Uniform Supersonic Chemical Reactors: 30 Years of Astrochemical History and Future Challenges

“…An important step forward was done in the late 2010s when the Leone research group in Berkeley connected the ALS synchrotron light with their CRESU machine to detect neutral products after photoionization and mass selection . For this they developed an airfoil‐shaped mass spectrometer set in front of the supersonic flow.…”

CRITICAL REVIEW OF N, N + , N + 2 , N ++ , And N ++ 2 MAIN PRODUCTION PROCESSES AND REACTIONS OF RELEVANCE TO TITAN'S ATMOSPHERE

“…The latest promising development is the use of the Advanced Light Source (ALS) at Berkeley which provides tuneable synchrotron radiation to photoionize the products from neutral-neutral reactions. The ionized products are then analyzed by time of flight or quadrupole mass spectrometry (Osborn et al 2008;Soorkia et al 2008). In addition, to our knowledge, no quantitative experimental investigations of the branching ratios of reactions involving atomic nitrogen have been made at low temperature.…”

Formation of fulvene in the reaction of C2H with 1,3-butadiene

“…Generally, in flow tube experiments, C 2 H is formed via 193 nm photolysis of C 2 H 2 , or occasionally 193 nm photolysis of trifluoromethylacetylene (CF 3 CCH). Recent work in our group has employed 193 nm photolysis of C 2 H 2 and CF 3 CCH to determine the products and rates of reactions of C 2 H with acetylene [32], ethene [33], propene [33], butenes [34], allene [35] and propyne [35], among others. However, polyunsaturated and acetylenic C 4 (and higher) hydrocarbons tend to absorb strongly at 193 nm, so there are concurrent photodissociation yields of radicals that can interfere with the reaction of interest or give rise to secondary reactions that complicate the analysis.…”