Absorption Spectrum of Nitrogen in the Region from 1075 to 1650 A

Time-resolved study of excited states of N2 near its first ionization threshold

Two-photon, two-color double-resonance ionization spectroscopy combining synchrotron vacuum ultraviolet radiation with a tunable near-infrared (NIR) laser has been used to investigate gerade symmetry states of the nitrogen molecule. The rotationally resolved spectrum of an autoionizing (1)Σ(g)(-) state has been excited via the intermediate c(4) (v = 0) (1)Π(u) Rydberg state. We present the analysis of the band located at T(v) = 10,800.7 ± 2 cm(-1) with respect to the intermediate state, 126,366 ± 11 cm(-1) with respect to the ground state, approximately 700 cm(-1) above the first ionization threshold. From the analysis a rotational constant of B(v) = 1.700 ± 0.005 cm(-1) has been determined for this band. Making use of the pulsed structure of the two radiation beams, lifetimes of several rotational levels of the intermediate state have been measured. We also report rotationally-averaged fluorescence lifetimes (300 K) of several excited electronic states accessible from the ground state by absorption of one photon in the range of 13.85-14.9 eV. The averaged lifetimes of the c(4) (0) and c(5) (0) states are 5.6 and 4.4 ns, respectively, while the b(') (12), c(')(4) (4, 5, 6), and c(')(5) (0) states all have lifetimes in the range of hundreds of picoseconds.

Factors affecting primary ionization in dopant-assisted atmospheric pressure photoionization (DA-APPI) for LC/MS

The sensitivity of dopant-assisted atmospheric pressure photoionization (DA-APPI) for LC/MS is generally reduced at higher solvent flow rates. Theory suggests that quenching of excited-state precursors to the dopant ions, via collisions with vaporized solvent molecules, may be one mechanism responsible for this trend. To ascertain if the primary rate of ionization is affected by quenching, experiments were performed utilizing an ionization detector to determine the primary ion current generated by irradiating vaporized mixtures of toluene dopant and methanol solvent. The results indicate that no loss of primary ion current occurs as the solvent flow is increased, provided the dopant-to-solvent ratio is held constant. Additional primary ion current can always be generated by increasing the dopant flow rate and/or the lamp power. Thus, quenching of excited-state precursors to the dopant ions, leading to a reduction in the primary rate of ionization, is not the mechanism responsible for the observed loss of sensitivity at higher liquid solvent flow rates.