Lifetime and predissociation yield of N214 b 1Πu(v=1)

Sprengers, J. P.; Ubachs, Wim; Johansson, Ann-Charlotte; L’Huillier, Anne; Wahlström, C.‐G.; Lang, R. W.; Lewis, B. R.; Gibson, S. T.

doi:10.1063/1.1704640

Cited by 38 publications

(52 citation statements)

References 34 publications

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“…The first quantitative model for the predissociation of the lowest b-state levels of N 2 , based on a coupled-channel Schrödinger-equation ͑CSE͒ treatment of the interacting b , c , o 1 ⌸ u , and C , CЈ 3 ⌸ u states, was developed by Lewis et al 5 Recently, Haverd et al 6 have extended this model to consider the effects of molecular rotation on the predissociation linewidths of the 1 ⌸ u levels and the band oscillator strengths for the 1 ⌸ u − X 1 ⌺ g + ͑v ,0͒ transitions, finding excellent agreement with the experimental data of Stark et al 7 Here, building on these recent developments, we perform CSE calculations of the J dependences of the radiative, predissociative, and total lifetimes of the b͑v =1͒ level of N 2 , and, by comparison with experiment, show that the apparent discrepancy between the results of Sprengers et al 4 and Oertel et al 1 is an artifact, caused by a significant J dependence of the lifetime, together with differing experimental conditions. This comparison is facilitated by the analysis of further EUV pump-probe data, not included in Ref.…”

supporting

confidence: 78%

“…3 The particular importance of b͑v =1͒ arises because it is the only b-state level which decays principally radiatively, rather than by predissociation. Recently, Sprengers et al 4 determined experimentally a lifetime of 2.61͑10͒ ns for this level, using an EUV-laser-based pump-probe scheme, and deduced a corresponding predissociation yield of ϳ28% following a semiempirical calculation of 3.61 ns for the radiative lifetime. The lifetime of Ref.…”

mentioning

confidence: 99%

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Lifetime and predissociation yield of N214bΠu1(v=1) revisited: Effects of rotation

Lewis

Gibson

Sprengers

et al. 2005

The Journal of Chemical Physics

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confidence: 78%

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confidence: 99%

Lifetime and predissociation yield of N214bΠu1(v=1) revisited: Effects of rotation

Lewis

Gibson

Sprengers

et al. 2005

The Journal of Chemical Physics

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“…The predissociation efficiency η is then given by η = 1−τ tot /τ rad , where τ tot is the inverse of the sum of the radiative and predissociation rates. For almost all transitions, η 1: significant corrections for partial dissociation are needed only for the b − X(1, 0) and c − X(0, 0) bands near 986 and 959 Å, respectively (Lewis et al 2005b;Liu et al 2008;Sprengers et al 2004;Wu et al 2012). For example, the top panel of Fig.…”

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%

Photodissociation of interstellar N₂

Heays

Visser

et al. 2013

A&A

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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.

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“…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

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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.

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Lifetime and predissociation yield of N214 b 1Πu(v=1)

Cited by 38 publications

References 34 publications

Lifetime and predissociation yield of N214bΠu1(v=1) revisited: Effects of rotation

Lifetime and predissociation yield of N214bΠu1(v=1) revisited: Effects of rotation

Photodissociation of interstellar N₂

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

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Lifetime and predissociation yield of N214 b 1Πu(v=1)

Cited by 38 publications

References 34 publications

Lifetime and predissociation yield of N214bΠu1(v=1) revisited: Effects of rotation

Lifetime and predissociation yield of N214bΠu1(v=1) revisited: Effects of rotation

Photodissociation of interstellar N2

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

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Photodissociation of interstellar N₂

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