FOURIER TRANSFORM ION CYCLOTRON RESONANCE DETECTION OF MULTIPHOTON IONIZATION SPECTROSCOPY

Abstract

Fourier transform ion cyclotron resonance (FT-ICR) detection was tested for resonance-enhanced multiphoton ionization (REMPI) spectroscopy. The (2 + 1) REMPI spectra of acetaldehyde were obtained in the wavelength range 364-354 nm via a two-photon resonant 3s <-- n Rydberg transition. The space-charge effects on the REMPI spectra were examined in the vicinity of the 0(0)(0) transition. The trapping efficiency measurement shows that all the ions produced from REMPI dissociation processes are arrested in the ion cyclotron resonance cell even in the presence of space-charge interactions. Axial kinetic energy release distributions of ions were extracted from the trapping efficiency data obtained under a new space-charge-free condition. ET-ICR peak heights were measured as a function of pressure at different laser powers, magnetic field strengths, and ion excitation methods to test for the detection linearity. The ET-ICR detection responds linearly to the number of ions in a low pressure limit. The product branching ratio was measured by using various ion excitation methods and was compared with the previous quadrupole mass spectrometric study. ET-ICR detection yields the mass-selected REMPI spectra and the product branching ratio in the absence of kinetic shifts.