Theoretical and experimental studies on concerted elimination of 1, 2‐bromochloroethane monocation to C2H4+ and BrCl

Abstract

AbstractAb initio calculations for the concerted elimination of 1, 2‐bromochloroethane monocation (1,2‐C2H4BrCl+) to C2H4+ and BrCl are performed using the Minnesota density functional M06‐2X and the def2‐TZVP basis set. Ab initio calculations are also carried out for the concerted elimination of 1,2‐C2H4BrCl+ to C2H4 and BrCl+ because the positive charge can be assigned to either moiety in the dissociative ionization process of 1,2‐C2H4BrCl+. Our results demonstrate that the concerted elimination channel of 1,2‐C2H4BrCl+ to C2H4+ and BrCl is preferred and that 1,2‐C2H4BrCl+ surpasses two energy barriers and then separates into C2H4+ + BrCl through an asynchronous concerted process. Experimentally, we confirm that this elimination channel is from the dissociative ionization process of 1,2‐C2H4BrCl+ by using dc‐slice imaging technique. The time‐of‐flight mass spectra of 1,2‐bromochloroethane induced by femtosecond laser pulses show that C2H4+ occurs at a laser intensity of 6.0 × 1013 W/cm2, and BrCl+ occurs at a higher laser intensity than C2H4+. This finding is consistent with the theoretical result that the appearance energy of C2H4+ is lower than that of BrCl+. As such, the low‐velocity component of BrCl+ is absent from our sliced images.