Mass-Analyzed Threshold Ionization (MATI) Spectroscopy of Atoms and Molecules Using VUV Synchrotron Radiation

Abstract

Mass-analyzed threshold ionization (MATI) spectroscopy using synchrotron radiation (Advanced Light Source, Lawrence Berkeley National Laboratory) has been performed for Ar, N(2), O(2), N(2)O, H(2)O, C(2)H(2), and C(6)H(6). MATI allows for a better determination of ionization energies compared to those derived from photoionization efficiency curves traditionally used in synchrotron photoionization mass spectrometry. The separation of the long-lived Rydberg state from the directly formed prompt ion, essential for a meaningful MATI spectrum, has been accomplished by employing an arrangement of ion optics coupled to unique electric field pulsing schemes. For Ar, a number of resolved bands below the ionization energy are observed, and these are ascribed to high-n,l Rydberg states prepared in the MATI scheme. The first vibrational state resolved MATI spectra of N(2) and O(2) are reported, and spectral characteristics are discussed in comparison with previously reported threshold photoelectron spectroscopic studies. Although MATI performed with synchrotron radiation is intrinsically less sensitive compared to laser-based sources, this work demonstrates that MATI spectroscopy performed with widely tunable vacuum ultraviolet (VUV) radiation is a complementary technique for studying the ionization spectroscopy of polyatomic molecules.