The hybrid density functional (U) B3LYP calculations with the 6-311++G (d,p) basis set were carried out for exploring the structures, stabilities, and H+-loss dissociation potential energy curves (PECs) for the C2H2n+ (n = 2, 3, and 4) ions without external fields and at different external electric field intensities. Without external electric fields, our calculations indicate that the C2H22+ and C2H23+ ions are stable, and the C2H24+ ion is unstable and spontaneously dissociates forming two carbon cations and two protons. The spontaneous dissociation of the C2H24+ ion is attributed to the Coulomb explosion. At the external electric field intensity of 0.06 a.u., the C2H22+ ion becomes unstable and spontaneously dissociates to C2H+ + H+. But for C2H23+, the field intensity of 0.0075 a.u will make it spontaneously dissociate to C2H2+ + H+. The spontaneous dissociations of C2H22+ and C2H23+ in the external electric field are attributed to the field-assisted dissociation. The adiabatic and vertical ionization energies from the C2H2 molecule to each of the C2H22+, C2H23+ and C2H24+ ions were also calculated without and at different external electric field intensities using the B3LYP method.

Key words: acetylene cation, density functional theory, field-assisted dissociation, coulomb explosion