Photoabsorption, photoionization, and neutral-dissociation cross sections of simple hydrocarbons in the vacuum ultraviolet range

Kameta, Kosei; Kouchi, Noriyuki; Ukai, Masatoshi; Hatano, Yoshihiko

doi:10.1016/s0368-2048(02)00022-1

Cited by 108 publications

(94 citation statements)

References 51 publications

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“…The absorption cross sections for CH 4 (Mount et al, 1977;Kameta et al, 2002;Chen and Wu, 2004) and N 2 (Chan et al, 1993) show that direct dissociation of N 2 is not expected in the FUV. The vertical dashed line indicates the lower limit of our lamp emission.…”

Section: Figmentioning

confidence: 99%

Nitrogen Incorporation in CH₄-N₂ Photochemical Aerosol Produced by Far Ultraviolet Irradiation

et al. 2012

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Nitrile incorporation into Titan aerosol accompanying hydrocarbon chemistry is thought to be driven by extreme UV wavelengths (k < 120 nm) or magnetospheric electrons in the outer reaches of the atmosphere. Far UV radiation (120-200 nm), which is transmitted down to the stratosphere of Titan, is expected to affect hydrocarbon chemistry only and not initiate the formation of nitrogenated species. We examined the chemical properties of photochemical aerosol produced at far UV wavelengths, using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), which allows for elemental analysis of particle-phase products. Our results show that aerosol formed from CH 4 /N 2 photochemistry contains a surprising amount of nitrogen, up to 16% by mass, a result of photolysis in the far UV. The proportion of nitrogenated organics to hydrocarbon species is shown to be correlated with that of N 2 in the irradiated gas. The aerosol mass greatly decreases when N 2 is removed, which indicates that N 2 plays a major role in aerosol production. Because direct dissociation of N 2 is highly improbable given the immeasurably low cross section at the wavelengths studied, the chemical activation of N 2 must occur via another pathway. Any chemical activation of N 2 at wavelengths > 120 nm is presently unaccounted for in atmospheric photochemical models. We suggest that reaction with CH radicals produced from CH 4 photolysis may provide a mechanism for incorporating N into the molecular structure of the aerosol. Further work is needed to understand the chemistry involved, as these processes may have significant implications for how we view prebiotic chemistry on early Earth and similar planets.

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Section: Figmentioning

confidence: 99%

Nitrogen Incorporation in CH₄-N₂ Photochemical Aerosol Produced by Far Ultraviolet Irradiation

et al. 2012

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“…Here, the experimental cross section of Kameta et al (2002) between 52 and 124 nm was used, and the slightly-lower resolution data of Au et al (1993) outside this range. The cross sections of Kameta et al (2002) was scaled down by a factor or 0.95 in order to agree with other more reliably calibrated overlapping measurements (Au et al 1993;Lee 2009). …”

Section: Ch 4 -Methanementioning

confidence: 99%

Photodissociation and photoionisation of atoms and molecules of astrophysical interest

Heays

Bosman

Dishoeck

2017

A&A

442

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A new collection of photodissociation and photoionisation cross sections for 102 atoms and molecules of astrochemical interest has been assembled, along with a brief review of the basic physical processes involved. These have been used to calculate dissociation and ionisation rates, with uncertainties, in a standard ultraviolet interstellar radiation field (ISRF) and for other wavelength-dependent radiation fields, including cool stellar and solar radiation, Lyman-α dominated radiation, and a cosmic-ray induced ultraviolet flux. The new ISRF rates generally agree within 30% with our previous compilations, with a few notable exceptions. Comparison with other databases such as PHIDRATES is made. The reduction of rates in shielded regions was calculated as a function of dust, molecular and atomic hydrogen, atomic C, and self-shielding column densities. The relative importance of these shielding types depends on the atom or molecule in question and the assumed dust optical properties. All of the new data are publicly available from the Leiden photodissociation and ionisation database. Sensitivity of the calculated rates to variation of temperature and isotope, and uncertainties in measured or calculated cross sections, are tested and discussed. Tests were conducted on the new rates with an interstellar-cloud chemical model, and find general agreement (within a factor of two) in abundances obtained with the previous iteration of the Leiden database assuming an ISRF, and order-of-magnitude variations assuming various kinds of stellar radiation. The newly parameterised dust-shielding factors makes a factor-of-two difference to many atomic and molecular abundances relative to parameters currently in the UDfA and KIDA astrochemical reaction databases. The newly-calculated cosmic-ray induced photodissociation and ionisation rates differ from current standard values up to a factor of 5. Under high temperature and cosmic-ray-flux conditions the new rates alter the equilibrium abundances of abundant dark cloud abundances by up to a factor of two. The partial cross sections for H 2 O and NH 3 photodissociation forming OH, O, NH 2 and NH are also evaluated and lead to radiation-field-dependent branching ratios.

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“…Total photoabsorption cross sections have been measured in the vacuum-UV range of 10-30 eV many times [21][22][23][24][25], with cross sections ranging from ca.…”

Section: Introductionmentioning

confidence: 99%

Vacuum-UV negative photoion spectroscopy of CH₄

Rogers¹,

Tuckett²,

Dunn³

et al. 2010

Molecular Physics

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_________________________________________________Using synchrotron radiation in the range 12−35 eV, negative ions are detected by mass spectrometry following vacuum-UV photoexcitation of methane. Ion yields for H − , CH − and CH 2 − are recorded, the spectra of CH − and CH 2 − for the first time. All ions display a linear dependence of signal with pressure, showing that they arise from unimolecular ion-pair dissociation. Cross sections for ion-pair formation are put onto an absolute scale by calibrating the signal strengths with those of F − from SF 6 and CF 4 .Following normalisation to total vacuum-UV absorption cross sections, quantum yields for anion production are reported. There is a major discrepancy in the H − cross section with an earlier measurement, which remains unresolved. The anions arise from both direct and indirect ion-pair mechanisms. increasing with increasing v in the ν 1 (a 1 ) vibrational ladder. They are the first direct measurement of an upper value to the dissociation rate of these levels into fragment ions.___________________________________________________

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Photoabsorption, photoionization, and neutral-dissociation cross sections of simple hydrocarbons in the vacuum ultraviolet range

Cited by 108 publications

References 51 publications

Nitrogen Incorporation in CH₄-N₂ Photochemical Aerosol Produced by Far Ultraviolet Irradiation

Nitrogen Incorporation in CH₄-N₂ Photochemical Aerosol Produced by Far Ultraviolet Irradiation

Photodissociation and photoionisation of atoms and molecules of astrophysical interest

Vacuum-UV negative photoion spectroscopy of CH₄

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Photoabsorption, photoionization, and neutral-dissociation cross sections of simple hydrocarbons in the vacuum ultraviolet range

Cited by 108 publications

References 51 publications

Nitrogen Incorporation in CH4-N2 Photochemical Aerosol Produced by Far Ultraviolet Irradiation

Nitrogen Incorporation in CH4-N2 Photochemical Aerosol Produced by Far Ultraviolet Irradiation

Photodissociation and photoionisation of atoms and molecules of astrophysical interest

Vacuum-UV negative photoion spectroscopy of CH4

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Nitrogen Incorporation in CH₄-N₂ Photochemical Aerosol Produced by Far Ultraviolet Irradiation

Nitrogen Incorporation in CH₄-N₂ Photochemical Aerosol Produced by Far Ultraviolet Irradiation

Vacuum-UV negative photoion spectroscopy of CH₄