Isomerization of linear C3H 3 + in its reaction with acetylene,and collisional stabilization of the [C5H 5 + ]* collision complex in a quadrupole ion trap mass spectrometer

The isomerization of linear C₃H ₃ ⁺ in its reaction with acetylene to cyclic C₃H ₃ ⁺ was studied with a quadrupole ion trap mass spectrometer. The reaction of linear C₃H ₃ ⁺ with ¹³C₂H₂ shows that isomerization takes place via a C₅H ₅ ⁺ ]^* activated complex that is unstable relative to disproportionation back into the cyclic and linear forms of C₃H ₃ ⁺ and acetylene. The formation of carbon-13 labeled cyclic and linear C,Hi indicates that isomerization involves skeletal exchange. Collisional stabilization of the C₅H ₅ ⁺ ]^* collision complex was achieved at a helium pressure of approximately 1 mtorr.