Threshold Collision-Induced Dissociation of Proton-Bound Hydrazine and Dimethylhydrazine Clusters

Threshold collision-induced dissociation (TCID) using a guided ion beam tandem mass spectrometer is performed on (N₂H₄)_nH⁺ where n = 2-4 and on the proton-bound unsymmetrical 1,1-dimethylhydrazine (UDMH) dimer complex. The primary dissociation pathway for all reactants consists of loss of a single hydrazine (or UDMH) molecule followed by the sequential loss of additional hydrazine molecules at higher collision energies for n = 3 and 4. The data were analyzed using a statistical model after accounting for internal and kinetic energy distributions, multiple collisions, and kinetic shifts to obtain 0 K bond dissociation energies (BDEs). These are also converted to values at room temperature by using a rigid rotor/harmonic oscillator approximation and theoretical molecular constants. Experimental BDEs are compared to theoretical BDEs determined at the B3LYP, M06, mPW1PW91, PBE0, MP2(full), and CCSD(T) levels of theory with and without empirical dispersion with a 6-311+G(2d,2p) basis set. The structures of all clusters are explored and exhibit extensive hydrogen bonding.