Furthermore, vibrationally resolved absorption spectra of the cations were computed at the (TD-)DFT level (UB3LYP/6-31G*) making use of the vertical gradient (VG) approximation . VG is a version of what is known as IMDHO, Independent Mode Displaced Harmonic Oscillator -the model which does not include frequency alteration and Duschinsky rotation -with the geometry shift being calculated without optimizing the excited state, but using instead the gradient of the excited state potential energy surface at the minimum geometry of the ground state. A higher level, e.g., adiabatic Hessian (AH), was not used because the TD-DFT excited state optimizations failed to converge. The vibrationally resolved spectra were computed in the Franck-Condon approximation employing the time-dependent (TD) formalism for spectroscopy (which is based on autocorrelation functions) as implemented in Gaussian 16. The default Gaussian 16 parameters were mostly used. In particular, a Gaussian broadening with half-width at half-maximum of 135 cm -1 was applied. For Ama + , a smaller time step and a larger number of steps were used [keywords TD=(2NStep=20,Time=1e-12)], since the default parameters resulted in nonphysical negative intensities for some transitions. The spectra were computed for temperature T = 0 K.