Rovibrationally selected ion-molecule reaction studies using the vacuum ultraviolet laser pulsed field ionization-photoion and guided ion beam methods.

摘要

We have successfully performed rovibrationally selected ion-molecule studies with translational energy in the center-of-mass ( Ecm) from thermal to 10 eV by implementing the Vacuum ultraviolet (VUV) laser-based pulsed field ionization-photoion (PFI-PI) experimental technique with the newly developed double quadrupole-double octopole (DQDO) apparatus in our laboratory. A novel electric pulsing sequence has been developed to prepare ions of interests in single rovibrational states with not only with high intensity but also high translational energy resolution. An unprecedented translational energy resolution as low as 0.05 eV in the laboratory frame (DeltaElab) is achieved that allows us to investigate the effect rotational, vibrational and translational energy on the chemical reactivity of ion-molecule reactions. Using VUV-PFI-PI technique we show that N2+ ions can be selected in v+ vibrational states from v+ = 0-2 and in a particular N + rotational levels from N+ = 0-9 at ground electronic state. Similarly, the triatomic H2O + ions can be prepared in the v1 +v2 +v 3 + = 000, 100 and 020 states and the N+ Ka+Kc+ = 000, 111, and 211 states, respectively, for rovibrationally selected ion-molecule reaction studies. Absolute integral cross sections (sigma), as well as branching ratios, as a function of both internal ro-vibrational and translational energies of ions, are obtained for the ion-molecule reactions of N2+( X2Sigmag+; v+ = 0-2; N+ = 0-9) + Ar/CH4 and H2O +(X2B1; v1 +v2 +v3 + = 000; N + Ka+Kc+ ) + D2/CO. Many fascinating phenomena about chemical reaction dynamics are observed for the first time. These include vibrational enhancements in the charge-transfer cross sections of N2+(X2Sigmag +; v+; N+) + Ar → Ar+ + N2, rotational enhancements in the chemical reactivity of H2O+(X2B1; v1 +v2 +v3 +; N+ Ka+Kc+ ) + D2 → H2DO+ + D, and distinct activation thresholds in the reaction of H2O+(X 2B1; v1 +v 2 +v3+; N + Ka+Kc+ ) + CO → CO+ + H2O. This kind of data is unique and it provides a database that serves as benchmarks for theoretical calculations and the modeling of related reaction systems.