Photoexcitation and predissociation intensities of the c′ 1∑u+ (v=3 and 4), c 1∏u (v=3 and 4), and b′ 1∑u+ (v=10, 12, 13, and 15) states of N2

Abstract

Articles you may be interested inA femtosecond velocity map imaging study on B-band predissociation in CH3I. II. The 2 0 1 and 3 0 1 vibronic levels High-resolution millimeter wave spectroscopy and multichannel quantum defect theory of the hyperfine structure in high Rydberg states of molecular hydrogen H 2 Photofragment spectroscopy is applied to investigate perturbations in the photoexcitation and predissociation of excited singlet states of N 2 . Discrete rovibrational levels in the Rydberg states cЈ 1 ͚ u ϩ (vϭ3 and 4͒ and c 1 ͟ u (vϭ3 and 4͒ and in the valence state bЈ 1 ͚ u ϩ (vϭ10, 12, 13, and 15͒ are prepared by laser excitation from the metastable aЉ 1 ͚ g ϩ (vϭ0) state in a fast ͑3 keV͒ molecular beam. Fragment atoms produced by predissociation are monitored as a function of exciting laser frequency using a position-and time-sensitive detector to measure the photofragment intensity distribution in the rovibrational bands. The photofragment spectra show extreme departures from normal rovibronic intensity distributions due to strong perturbations in the two highly mixed complexes: cЈ(3)/c(3)/bЈ(10) and cЈ(4)/c(4)/bЈ(13). The measured photofragment intensities are compared to photoexcitation line strengths calculated using a comprehensive model of the Rydberg-valence state mixing ͓Stahel, Leoni, and Dressler, J. Chem. Phys. 79, 2541 ͑1983͔͒. This theoretical model accurately predicts most of the variations in the photofragment intensities, and reveals the causes of the perturbations. For the states investigated in the present study, the primary factor that determines the photofragment intensity is the degree of bЈ character of the state, which favorably affects both photoexcitation and predissociation. Interference effects are found to be important in determining absorption intensities in N 2 .

Branching Ratios in Vacuum Ultraviolet Photodissociation of CO and N2: Implications for Oxygen and Nitrogen Isotopic Compositions of the Solar Nebula

“…Recent work in our laboratory has shown that direct singlephoton excitation with a VUV laser from low rotational levels of N 2 (X 1 Σ g + ) produces only atoms N( 4 S) + N( 2 D) from reaction (2) 11.09-13.60 eV (91.17-111.78 nm) (Gao et al 2011b;Pan et al 2011;Song et al 2016). This observation is in agreement with the early studies (Helm & Cosby 1989;Walter et al 1993Walter et al , 2000 using visible laser excitation of higher rotational levels of the N 2 (a″…”

“…The D 0 (N 2 ) is 9.7537±0.0011 eV (127.12-0.02/+0.01 nm) (Tang et al 2005) and thus, there are three accessible energetically allowed dissociation channels (1)-(3), in the energy interval between 9.75-13.60 eV (91.17-127.12 nm): Previous photodissociation studies reported that reaction (1) is negligible (e.g., Helm & Cosby 1989;Walter et al 1993Walter et al , 2000. However, these studies involved high rotational levels of excited predissociative states of N 2 , whereas low rotational levels are of interest in astronomical environments.…”

Indirect predissociation of highly excited singlet states of N2

“…1 wherever there is a near degeneracy of valence and Rydberg states. Rotational interactions are also known to mix the 1 u and 1 + u states, leading to energy-level perturbations near crossing points in their rotational progressions, and accompanying intensity interference effects [5,6,18].…”

Isotopic variation of experimental lifetimes for the lowest Πu1 states of N2

“…1 The absorption is associated with dipole-allowed excitation of singlet ungerade ͑c n Ј 1 ⌺ u + , bЈ 1 ⌺ u + , c n 1 ⌸ u , o n 1 ⌸ u , and b 1 ⌸ u , where n is the principal quantum number͒ states, which are known to undergo strong predissociation, [2][3][4][5][6][7][8][9][10][11][12] some showing rotational dependence. 13 The rates of predissociation of these levels are key inputs in the radiation budget of the Earth's atmosphere, but the applicable predissociation mechanisms are far from being understood at present.…”

“…14 Lifetimes of the singlet ungerade states in N 2 have been measured using a wide variety of sophisticated experimental techniques. Laser-induced photofragment translational spectroscopy was performed in various studies 4,[6][7][8]10,12 that also provided direct information on the predissociation yields. Direct time domain studies have also been performed, either via the delayed coincidence technique combined with synchrotron radiation, 15 or via a vacuum ultraviolet-laser based pump-probe technique.…”