Vibrationally resolved photoionization of N2 near threshold

Abstract

A recently developed velocity map imaging spectrometer has been used to study the photoionization of molecular nitrogen near threshold. The potentialities of the spectrometer have been exploited to measure simultaneously the energy and angular distribution of the photoelectrons corresponding to the residual N(2)(+) X(2)Σ(g) v = 0-3 ion states. In a single experiment all the experimental observables, i.e., the total and partial cross sections, their branching ratios and the asymmetry parameter of the angular distributions have been determined.

Photoelectron angular distributions from rotationally resolved autoionizing states of N2

“…Perhaps the most noteworthy of these regions lies between ∼126 200 and 126 500 cm 1 in the single-photon ionization spectrum. 1,[5][6][7][14][15][16][17] This region contains a number of sharp bands along with two intense, broad-yet-structured, complex resonances that have been said to have the appearance of two towers of a gothic cathedral. There is substantial agreement over the assignment of most of the sharp structure, and the lower energy tower has been assigned to a transition associated with the (B 2 Σ u + )3sσ, v = 0 final state; however, despite numerous theoretical 4,9,14,15 and experimental studies, no consensus has been reached for the assignment of the higher energy tower.…”

“…17 In principle, photoelectron angular distributions can provide insight into the photoionization dynamics and the electronic character of the autoionizing resonances and ejected photoelectron. 6,7,[19][20][21][22][23][24][25] Such studies are most informative when the excitation process is rotationally resolved and when the final ionic state is vibrationally and rotationally resolved. [26][27][28][29][30] There have been a number of previous studies of the photoelectron angular distributions of N 2 just above the first ionization threshold.…”

“…[26][27][28][29][30] There have been a number of previous studies of the photoelectron angular distributions of N 2 just above the first ionization threshold. In recent studies by O'Keeffe et al 6 and Holland et al, 7 velocity map imaging was used to record photoelectron energy and angular distributions as a function of wavelength between threshold and ∼135 000 cm 1 . In this region, the N 2 + ion can be left in the X 2 Σ g + state with v + ≤ 4, and the electron energy resolution 6,7 was sufficient to resolve vibrational, but (for the most part) not rotational, levels of the ion.…”

“…[1][2][3][4][5][6][7] This relatively large number of states can lead to complex resonance features that are perturbed with respect to intensities, linewidths, and expected level positions. Thus, while considerable progress has been made in the analysis of this region of the N 2 spectrum, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] some strong features still lack definitive spectral assignments. Perhaps the most noteworthy of these regions lies between ∼126 200 and 126 500 cm 1 in the single-photon ionization spectrum.…”

“…[1][2][3][4][5][6][7] Between the ionization threshold 8 and ∼127 850 cm 1 , autoionization is energetically constrained to leave the ion in the N 2 + X 2 Σ g + , v + = 0 state. In this region, autoionization features arise from several different sources: autoionization of Rydberg series converging to vibrationally excited levels of the N 2 + X 2 Σ g + ground state; autoionization of Rydberg series converging to electronically excited states of N 2 + (notably the A 2 Π u and B 2 Σ u + states); and autoionization of high vibrational levels of the b 1 Σ u + and b 1 Π u valence states.…”