Structure and predissociation of the 3pσuD Σ3u+ Rydberg state of N2: First extreme-ultraviolet and new near-infrared observations, with coupled-channels analysis

Lewis, B. R.; Baldwin, K. G. H.; Heays, A. N.; Gibson, S. T.; Sprengers, J. P.; Ubachs, Wim; Fujitake, Masaharu

doi:10.1063/1.3023034

Cited by 15 publications

(21 citation statements)

References 28 publications

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“…To demonstrate the utility of the INMS ion densities derived as described in this paper to evaluate and improve models of Titan's atmosphere, we updated the model described by De La Haye et al [2008] (INT08 in Table 8) by including chemical reactions from more recent publications [i.e., Vuitton et al , 2006, 2007; Carrasco et al , 2008a; Krasnopolsky , 2009] and high‐resolution temperature‐dependent cross‐sections for N 2 and its isotope 14 N 15 N computed here using the coupled‐channel Schrödinger‐equation technique [ Lewis et al , 2005a, 2005b, 2008a, 2008b; Haverd et al , 2005; Ndome et al , 2008; Heays , 2010]. Neither INT08 nor the updated model, INT12, determine errors associated with calculations based on uncertainties of different parameters used in the model such as rate constants, cross‐sections, and branching ratios.…”

Section: Constraining Photochemical Models With Inms Ion Densitiesmentioning

confidence: 99%

Ion densities and composition of Titan's upper atmosphere derived from the Cassini Ion Neutral Mass Spectrometer: Analysis methods and comparison of measured ion densities to photochemical model simulations

et al. 2012

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.[1] The Cassini Ion Neutral Mass Spectrometer (INMS) has measured both neutral and ion species in Titan's upper atmosphere and ionosphere and the Enceladus plumes. Ion densities derived from INMS measurements are essential data for constraining photochemical models of Titan's ionosphere. The objective of this paper is to present an optimized method for converting raw data measured by INMS to ion densities. To do this, we conduct a detailed analysis of ground and in-flight calibration to constrain the instrument response to ion energy, the critical parameter on which the calibration is based. Data taken by the Cassini Radio Plasma Wave Science Langmuir Probe and the Cassini Plasma Spectrometer Ion Beam Spectrometer are used as independent measurement constraints in this analysis. Total ion densities derived with this method show good agreement with these data sets in the altitude region ($1100-1400 km) where ion drift velocities are low and the mass of the ions is within the measurement range of the INMS (1-99 Daltons). Although ion densities calculated by the method presented here differ slightly from those presented in previous INMS publications, we find that the implications for the science presented in previous publications is mostly negligible. We demonstrate the role of the INMS ion densities in constraining photochemical models and find that (1) cross sections having high resolution as a function of wavelength are necessary for calculating the initial photoionization products and (2) there are disagreements between the measured ion densities representative of the initial steps in Titan photochemistry that require further investigation. , et al. (2012), Ion densities and composition of Titan's upper atmosphere derived from the Cassini Ion Neutral Mass Spectrometer: Analysis methods and comparison of measured ion densities to photochemical model simulations,

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Section: Constraining Photochemical Models With Inms Ion Densitiesmentioning

confidence: 99%

Ion densities and composition of Titan's upper atmosphere derived from the Cassini Ion Neutral Mass Spectrometer: Analysis methods and comparison of measured ion densities to photochemical model simulations

et al. 2012

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“…This work considered in detail the sharply structured absorption spectrum of N 2 and shielding species. This was made possible by means of an accurate and comprehensive quantum-mechanical model of N 2 photoabsorption and dissociation, which was informed by an extensive history of N 2 spectroscopy in the laboratory (e.g., Ajello et al 1989;Helm et al 1993;Sprengers et al 2003Sprengers et al , 2004Sprengers et al , 2005aStark et al 2008;Lewis et al 2008b;Heays et al 2009 and theoretically (e.g., Spelsberg & Meyer 2001;Lewis et al 2005bLewis et al ,a, 2008aHaverd et al 2005;Ndome et al 2008). This model, detailed in Sect.…”

Section: Introductionmentioning

confidence: 99%

Isotope selective photodissociation of N₂by the interstellar radiation field and cosmic rays

Heays

Visser

Gredel

et al. 2014

A&A

102

130

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Context. Photodissociation of 14 N 2 and 14 N 15 N occurs in interstellar clouds, circumstellar envelopes, protoplanetary discs, and other environments due to ultraviolet radiation originating from stellar sources and the presence of cosmic rays. This source of N atoms initiates the formation of more complex N-bearing species and may influence their isotopic composition. Aims. We study the photodissociation rates of 14 N 15 N by ultraviolet continuum radiation and both isotopologues in a field of cosmic ray induced photons. To determine the effect of these on the isotopic composition of more complex molecules. Methods. High-resolution theoretical photodissociation cross sections of N 2 are used from an accurate and comprehensive quantummechanical model of the molecule based on laboratory experiments. A similarly high-resolution spectrum of H 2 emission following interactions with cosmic rays has been constructed. The spectroscopic data are used to calculate photodissociation rates which are then input into isotopically differentiated chemical models, describing an interstellar cloud and a protoplanetary disc. N 2 , H 2 , and H are presented. Incorporating these into an interstellar cloud model, an enhancement of the atomic 15 N/ 14 N ratio over the elemental value is obtained due to the self-shielding of external radiation at an extinction of about 1.5 mag. This effect is larger where assumed grain growth has reduced the opacity of dust to ultraviolet radiation. The transfer of photolytic isotopic fractionation of N and N 2 to other molecules is demonstrated to be significant in a protoplanetary disc model with grain growth, and is species dependent with 15 N enhancement approaching a factor of 10 for HCN. The cosmic ray induced dissociation of CO is revisited employing a more recent photodissociation cross section, leading to a rate that is ∼40% lower than previously calculated.

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“…This difference will be cardinal to what follows. The valence states are the gateway to dissociation via the repulsive triplet states (33)(34)(35)(36)(37)(38) that cannot be optically directly accessed from the ground state. Essentially the same comments apply to the UV excited states of the isoelectronic molecule CO. Ref.…”

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confidence: 99%

On the strong and selective isotope effect in the UV excitation of N ₂ with implications toward the nebula and Martian atmosphere

Muskatel

Remacle

Thiemens

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Isotopic effects associated with molecular absorption are discussed with reference to natural phenomena including early solar system processes, Titan and terrestrial atmospheric chemistry, and Martian atmospheric evolution. Quantification of the physicochemical aspects of the excitation and dissociation processes may lead to enhanced understanding of these environments. Here we examine a physical basis for an additional isotope effect during photolysis of molecular nitrogen due to the coupling of valence and Rydberg excited states. The origin of this isotope effect is shown to be the coupling of diabatic electronic states of different bonding nature that occurs after the excitation of these states. This coupling is characteristic of energy regimes where two or more excited states are nearly crossing or osculating. A signature of the resultant isotope effect is a window of rapid variation in the otherwise smooth distribution of oscillator strengths vs. frequency. The reference for the discussion is the numerical solution of the time dependent Schrödinger equation for both the electronic and nuclear modes with the light field included as part of the Hamiltonian. Pumping is to all extreme UV dipole-allowed, valence and Rydberg, excited states of N 2 . The computed absorption spectra are convoluted with the solar spectrum to demonstrate the importance of including this isotope effect in planetary, interstellar molecular cloud, and nebular photochemical models. It is suggested that accidental resonance with strong discrete lines in the solar spectrum such as the CIII line at 97.703 nm can also have a marked effect.photodissociation | isotopic fractionation | UV photodissociation P hotochemical processes are particularly pervasive in nature. Measurements of isotopic compositions provide insights into a range of such processes, both terrestrial and extraterrestrial. To adequately interpret such measurements, characterization of relevant isotopically selective physicochemical processes associated with gas phase processes is desirable. In this paper we quantify an isotopic selectivity due to electronic reorganization following ligfht absorption. The results are compared to the solar spectrum for applications in nature.There are a number of photodissociation processes that have been suggested where a more basic understanding of isotope effects could aid in the development of models. A striking example of observed, but presently not fully understood oxygen isotopic distribution occurs in the high temperature calcium aluminum rich inclusions of the Allende meteorite (1) and most oxygen bearing meteorites (see, for example, review in ref.2). Although originally thought to be nucleosynthetic in origin based upon laboratory experiments, it was later suggested that the observed isotopic composition might arise from photochemical self-shielding (3-6). It has also been proposed that given the special properties of oxygen, symmetry related properties might produce the same fraction in the actual mineral formation process (7-11). A...

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Structure and predissociation of the 3pσuD Σ3u+ Rydberg state of N2: First extreme-ultraviolet and new near-infrared observations, with coupled-channels analysis

Cited by 15 publications

References 28 publications

Ion densities and composition of Titan's upper atmosphere derived from the Cassini Ion Neutral Mass Spectrometer: Analysis methods and comparison of measured ion densities to photochemical model simulations

Ion densities and composition of Titan's upper atmosphere derived from the Cassini Ion Neutral Mass Spectrometer: Analysis methods and comparison of measured ion densities to photochemical model simulations

Isotope selective photodissociation of N₂by the interstellar radiation field and cosmic rays

On the strong and selective isotope effect in the UV excitation of N ₂ with implications toward the nebula and Martian atmosphere

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Structure and predissociation of the 3pσuD Σ3u+ Rydberg state of N2: First extreme-ultraviolet and new near-infrared observations, with coupled-channels analysis

Cited by 15 publications

References 28 publications

Ion densities and composition of Titan's upper atmosphere derived from the Cassini Ion Neutral Mass Spectrometer: Analysis methods and comparison of measured ion densities to photochemical model simulations

Ion densities and composition of Titan's upper atmosphere derived from the Cassini Ion Neutral Mass Spectrometer: Analysis methods and comparison of measured ion densities to photochemical model simulations

Isotope selective photodissociation of N2by the interstellar radiation field and cosmic rays

On the strong and selective isotope effect in the UV excitation of N 2 with implications toward the nebula and Martian atmosphere

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Isotope selective photodissociation of N₂by the interstellar radiation field and cosmic rays

On the strong and selective isotope effect in the UV excitation of N ₂ with implications toward the nebula and Martian atmosphere