A coupled-channel model of the Π3u states of N2: Structure and interactions of the 3sσgF3 Π3u and 3pπuG3 Π3u Rydberg states

Lewis, B. R.; Heays, A. N.; Gibson, S. T.; Lefebvre‐Brion, H.; Lefèbvre, R.

doi:10.1063/1.2990656

Cited by 68 publications

(105 citation statements)

References 38 publications

Supporting

Mentioning

100

Contrasting

Order By: Relevance

“…For the 1 Π u states considered here, spinorbit coupling to the strongly-coupled and -predissociated 3 Π u manifold (red PECs in Fig. 1), with ultimate dissociation via the C state, provides the predissociation mechanism (Lewis et al 2005a(Lewis et al , 2008c, with a minor contribution from a crossing by the 2 3 Σ + u state (green PEC in Fig. 1) at higher energies.…”

Section: Photoabsorption and Photodissociation Spectrummentioning

confidence: 99%

“…The same cannot be said for the line-by-line models such as those employed for CO, which would also benefit from a CSE approach. The detailed CSE model for N 2 employed here has been described in 1 incorporates earlier models of the 1 Π u (Lewis et al 2005a;Haverd et al 2005) and 3 Π u states (Lewis et al 2008c) and has been tested extensively against laboratory data, including high-resolution spectra obtained at the SOLEIL synchrotron facility . A complete discussion of the CSE model and a full listing of computed spectroscopic data is deferred to Heays et al (in prep.).…”

Section: Photoabsorption and Photodissociation Spectrummentioning

confidence: 99%

“…Moreover, these lines can be shielded by lines of more abundant species such as H, H 2 and CO. Until recently, accurate N 2 molecular data to simulate these processes were not available. Thanks to a concerted laboratory (e.g., Ajello et al 1989;Helm et al 1993;Sprengers et al 2003Sprengers et al , 2004Sprengers et al , 2005Stark et al 2008;Lewis et al 2008b;Heays et al 2009 and theoretical (e.g., Spelsberg & Meyer 2001;Lewis et al 2005aLewis et al ,b, 2008cHaverd et al 2005;Ndome et al 2008) effort over the past two decades, this information is now available.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Photodissociation of interstellar N₂

Heays

Visser

et al. 2013

A&A

Self Cite

138

View full text Add to dashboard Cite

Context. Molecular nitrogen is one of the key species in the chemistry of interstellar clouds and protoplanetary disks, but its photodissociation under interstellar conditions has never been properly studied. The partitioning of nitrogen between N and N 2 controls the formation of more complex prebiotic nitrogen-containing species. Aims. The aim of this work is to gain a better understanding of the interstellar N 2 photodissociation processes based on recent detailed theoretical and experimental work and to provide accurate rates for use in chemical models. Methods. We used an approach similar to that adopted for CO in which we simulated the full high-resolution line-by-line absorption + dissociation spectrum of N 2 over the relevant 912-1000 Å wavelength range, by using a quantum-mechanical model which solves the coupled-channels Schrödinger equation. The simulated N 2 spectra were compared with the absorption spectra of H 2 , H, CO, and dust to compute photodissociation rates in various radiation fields and shielding functions. The effects of the new rates in interstellar cloud models were illustrated for diffuse and translucent clouds, a dense photon dominated region and a protoplanetary disk. Results. The unattenuated photodissociation rate in the Draine (1978, ApJS, 36, 595) radiation field assuming an N 2 excitation temperature of 50 K is 1.65 × 10 −10 s −1 , with an uncertainty of only 10%. Most of the photodissociation occurs through bands in the 957-980 Å range. The N 2 rate depends slightly on the temperature through the variation of predissociation probabilities with rotational quantum number for some bands. Shielding functions are provided for a range of H 2 and H column densities, with H 2 being much more effective than H in reducing the N 2 rate inside a cloud. Shielding by CO is not effective. The new rates are 28% lower than the previously recommended values. Nevertheless, diffuse cloud models still fail to reproduce the possible detection of interstellar N 2 except for unusually high densities and/or low incident UV radiation fields. The transition of N → N 2 occurs at nearly the same depth into a cloud as that of C + → C → CO. The orders-of-magnitude lower N 2 photodissociation rates in clouds exposed to black-body radiation fields of only 4000 K can qualitatively explain the lack of active nitrogen chemistry observed in the inner disks around cool stars. Conclusions. Accurate photodissociation rates for N 2 as a function of depth into a cloud are now available that can be applied to a wide variety of astrophysical environments.

show abstract

Section: Photoabsorption and Photodissociation Spectrummentioning

confidence: 99%

Section: Photoabsorption and Photodissociation Spectrummentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Photodissociation of interstellar N₂

Heays

Visser

et al. 2013

A&A

Self Cite

138

View full text Add to dashboard Cite

show abstract

“…We here employ the latest reported photodissociation rate and shielding functions for N 2 (Li et al 2013;Heays et al 2014) to investigate the effects in a chemical model of the CSE of IRC +10216. These are based on a concerted laboratory (e.g., Ajello et al 1989;Helm et al 1993;Sprengers et al 2004;Stark et al 2008;Lewis et al 2008a;Heays et al 2011) and theoretical (e.g., Spelsberg & Meyer 2001;Lewis et al 2005;2008b;Ndome et al 2008) effort over the last two decades. An update was also made to the photodissociation of CO using the selfshielding functions from Visser et al (2009) following a similarly large experimental effort over the past decades.…”

Section: Introductionmentioning

confidence: 99%

Photodissociation and chemistry of N₂in the circumstellar envelope of carbon-rich AGB stars

Millar

Walsh

et al. 2014

A&A

View full text Add to dashboard Cite

Context. The envelopes of asymptotic giant branch (AGB) stars are irradiated externally by ultraviolet photons; hence, the chemistry is sensitive to the photodissociation of N 2 and CO, which are major reservoirs of nitrogen and carbon, respectively. The photodissociation of N 2 has recently been quantified by laboratory and theoretical studies. Improvements have also been made for CO photodissociation. Aims. For the first time, we use accurate N 2 and CO photodissociation rates and shielding functions in a model of the circumstellar envelope of the carbon-rich AGB star, IRC +10216. Methods. We use a state-of-the-art chemical model of an AGB envelope, the latest CO and N 2 photodissociation data, and a new method for implementing molecular shielding functions in full spherical geometry with isotropic incident radiation. We compare computed column densities and radial distributions of molecules with observations. Results. The transition of N 2 → N (also, CO → C → C + ) is shifted towards the outer envelope relative to previous models. This leads to different column densities and radial distributions of N-bearing species, especially those species whose formation/destruction processes largely depend on the availability of atomic or molecular nitrogen, for example, C n N (n = 1, 3, 5), C n N − (n = 1, 3, 5), HC n N (n = 1, 3, 5, 7, 9), H 2 CN and CH 2 CN. Conclusions. The chemistry of many species is directly or indirectly affected by the photodissociation of N 2 and CO, especially in the outer shell of AGB stars where photodissociation is important. Thus, it is important to include N 2 and CO shielding in astrochemical models of AGB envelopes and other irradiated environments. In general, while differences remain between our model of IRC +10216 and the observed molecular column densities, better agreement is found between the calculated and observed radii of peak abundance.

show abstract

“…The high temperature (200 and 300 K) profiles show a peak in 15 Figure 3 shows the crowded electronic state diagram (diabatic representation) of N 2 depicting significant electrostatic interaction among the different symmetry states apart from the intrinsic configurational mixing within a symmetry group. [15][16][17][18][19] N 2 absorbs photons through slightly broadened partly overlapping rovibrational lines of excited singlet states. Most of the rovibrational levels of the singlet excited states are predissociative.…”

Section: Resultsmentioning

confidence: 99%

Nitrogen isotopic fractionations in the low temperature (80 K) vacuum ultraviolet photodissociation of N2

Chakraborty

Jackson

Rude

et al. 2016

The Journal of Chemical Physics

View full text Add to dashboard Cite

N2 is a diatomic molecule with complex electronic structure. Interstate crossings are prominent in the high energy domain, introducing significant perturbations to the system. Nitrogen mainly photodissociates in the vacuum ultraviolet (VUV) region of the electromagnetic spectrum through both direct and indirect predissociation. Due to the complexity introduced by these perturbations, the nitrogen isotopic fractionation in N2 photodissociation is extremely hard to calculate, and an experimental approach is required. Here we present new data of N-isotopic fractionation in N2 photodissociation at low temperature (80 K), which shows a distinctly different 15N enrichment profile compared to that at relatively higher temperatures (200 and 300 K). The new data, important to understanding the N-isotopic compositions measured in meteorites and other planetary bodies, are discussed in light of the knowledge of N2 photochemistry and calculated photoabsorption cross sections in the VUV.

show abstract

A coupled-channel model of the Π3u states of N2: Structure and interactions of the 3sσgF3 Π3u and 3pπuG3 Π3u Rydberg states

Cited by 68 publications

References 38 publications

Photodissociation of interstellar N₂

Photodissociation of interstellar N₂

Photodissociation and chemistry of N₂in the circumstellar envelope of carbon-rich AGB stars

Nitrogen isotopic fractionations in the low temperature (80 K) vacuum ultraviolet photodissociation of N2

Contact Info

Product

Resources

About

A coupled-channel model of the Π3u states of N2: Structure and interactions of the 3sσgF3 Π3u and 3pπuG3 Π3u Rydberg states

Cited by 68 publications

References 38 publications

Photodissociation of interstellar N2

Photodissociation of interstellar N2

Photodissociation and chemistry of N2in the circumstellar envelope of carbon-rich AGB stars

Nitrogen isotopic fractionations in the low temperature (80 K) vacuum ultraviolet photodissociation of N2

Contact Info

Product

Resources

About

Photodissociation of interstellar N₂

Photodissociation of interstellar N₂

Photodissociation and chemistry of N₂in the circumstellar envelope of carbon-rich AGB stars