Improved tandem mass spectrometer coupled to a laser vaporization cluster ion source

We describe two improvements to an existing tandem mass spectrometer coupled to a laser vaporization cluster ion source suitable for photodissociation spectroscopy: (i) cooling of the cluster source nozzle and (ii) mass selection prior to the photodissociation region via replacing an octupole ion guide by a quadrupole mass spectrometer. The improved sensitivity and transmission enable the production of larger heteroatomic clusters as well as rare gas solvated clusters. We present two examples demonstrating the new capabilities of the improved setup. In the first application, cooling of the cluster source nozzle produces Si⁺Ar_n and Si₂⁺Ar_n cluster cations with n = 1-25. Magic numbers are extracted from the mass spectrum by applying a transmission function obtained via simulations. In the second example, the vibronic photodissociation spectrum of cold Au₄⁺ cluster ions is recorded with unprecedented detail, resolution, and sensitivity. Such high-resolution optical excitation spectra of metal cluster cations may serve as a benchmark for the performance of Franck-Condon simulations based on quantum chemical calculations for excited states.