Fluorescence from photofragments as an aid in identifying new molecular states: The N2 case

Observation of new Rydberg series in the many-electron transition region of N2

Fluorescence excitation spectra produced through photoexcitation of N(2) using synchrotron radiation in the spectral region between 50 and 62.5 nm have been obtained with a resolution of 0.004 nm. A broadband detector (in the 115-180 nm region) was employed to monitor fluorescence originated from neutral excited atomic nitrogen fragments which are produced through direct dissociation processes and predissociation from the well-known many-electron excited Rydberg states. We have identified a new Rydberg series (2 (2)Π(g)) 4sσ, a better resolved Rydberg (D (2)Π(g)) npσ series, and also the prominent Codling series converging to the D (2)Π(g), and C (2)Σ(u)(+) states of N(2)(+), respectively. By normalizing our relative fluorescence intensities to previously measured absolute fluorescence cross-section data we obtain the cross-section data of undispersed fluorescence in the 115-180 nm region. The fluorescence quantum yields for the present photodissociative excitation processes are found to be less than 0.05. The present results may provide important data for our understanding of competitions among the various decay channels of the many-electron transition states of N(2).

Fluorescence excitation spectra of the bΠu1, b′Σu+1, cnΠu1, and cn′Σu+1 states of N2 in the 80–100nm region

Fluorescence excitation spectra produced through photoexcitation of N(2) using synchrotron radiation in the spectral region between 80 and 100 nm have been studied. Two broadband detectors were employed to simultaneously monitor fluorescence in the 115-320 nm and 300-700 nm regions, respectively. The peaks in the vacuum ultraviolet fluorescence excitation spectra are found to correspond to excitation of absorption transitions from the ground electronic state to the b (1)Pi(u), b(') (1)Sigma(u) (+), c(n) (1)Pi(u) (with n=4-8), c(n) (') (1)Sigma(u) (+) (with n=5-9), and c(4) (')(v('))(1)Sigma(u) (+) (with v(')=0-8) states of N(2). The relative fluorescence production cross sections for the observed peaks are determined. No fluorescence has been produced through excitation of the most dominating absorption features of the b-X transition except for the (1,0), (5,0), (6,0), and (7,0) bands, in excellent agreement with recent lifetime measurements and theoretical calculations. Fluorescence peaks, which correlate with the long vibrational progressions of the c(4) (') (1)Sigma(u) (+) (with v(')=0-8) and the b(') (1)Sigma(u) (+) (with v(') up to 19), have been observed. The present results provide important information for further unraveling of complicated and intriguing interactions among the excited electronic states of N(2). Furthermore, solar photon excitation of N(2) leading to the production of c(4) (')(0) may provide useful data required for evaluating and analyzing dayglow models relevant to the interpretation of c(4) (')(0) in the atmospheres of Earth, Jupiter, Saturn, Titan, and Triton.

Triton: topside ionosphere and nitrogen escape

The principal ion in the ionosphere of Triton is N+. Energetic electrons of magnetospheric origin are the primary source of ionization, with a smaller contribution due to photoionization. To explain the topside plasma scale height, we postulate that N+ ions escape from Triton. The loss rate is 3.4 x 10(7) cm-2 s-1 or 7.9 x 10(24) ions s-1. Dissociative recombination of N2+ produces neutral exothermic fragments that can escape from Triton. The rate is estimated to be 8.6 x 10(6) N cm-2 s-1 or 2.0 x 10(24) atoms s-1. Implications for the magnetosphere of Neptune and Triton's evolution are discussed.