Experiments were performed on an Agilent 6560 DTIMS-Q-TOF instrument (Agilent Technologies, Santa Clara, CA), equipped with the dual-ESI source operated in the negative ion mode. The pre-IMS introduction conditions were optimized for softness as described elsewhere. Note that the fragmentor is different for the present work: an electrode was introduced between the capillary and high-pressure funnel with small distance compared to the previous configuration, so the field generated at a given "fragmentor" value is greater than in reference . The drift tube was filled with helium and the pressure was fixed at 3.89 ± 0.01 Torr, measured accurately by a capacitance diaphragm gauge (CDG-500, Agilent Technologies). The following default IMS parameters were used: fragmentor voltage 320 V, trap fill time 1000 μs, trap release time 100 μs, trap entrance grid delta (TEGD) 2 V. For the CCS determination, the step-field experiment included 5 segments (1 min each) where drift tube entrance voltage was -650 V, -700 V, -800 V, -900, V, -1000 V. For CIU experiments, the drift tube entrance voltage was fixed at -650 V, and the activation was performed by varying the fragmentor voltage from 320 to 450 V.