a frequency-driven ion trap section operable to trap sample ions and isolate a precursor ion from said sample ions, while setting an ion-trapping RF voltage waveform at a first frequency providing a first low-mass cutoff (LMCO) value, and, then after setting the ion-trapping RF voltage waveform at a second frequency greater than said first frequency to provide a second LMCO value less than said first LMCO value, to irradiate said precursor ion in a tapped state with light so as to photodissociate said precursor ion into fragment ions; and

an analyzer section operable to subject said fragment ions ejected from said ion trap section, to mass spectrometry so as to obtain information about a molecular structure of said precursor ion.