Oxygen isotope fractionation in the vacuum ultraviolet photodissociation of carbon monoxide: Wavelength, pressure, and temperature dependency

Abstract

Several absorption bands exist in the VUV region of Carbon monoxide (CO). Emission spectra indicate that these bands are all predissociative. An experimental investigation of CO photodissociation by vacuum ultraviolet photons (90 to 108 nm; ~13 to 11 eV) from the

Use of Isotope Effects To Understand the Present and Past of the Atmosphere and Climate and Track the Origin of Life

“…X 1 A 1 ): SO 2 will be excited to at riplet state.T he first absorption band is difficult to investigate because there was no photocell window or laboratory light source available.Aseries of synchrotron experiments applied to varying molecules (CO,N 2 ,a nd H 2 S) [60-62, 64, 65, 144] open new areas for studying photochemically-induce isotope effects in the VUV range and investigation of SO 2 is currently underway. As shown in existing experiments,f or not only SO 2 [142,148] but also CO [61] and N 2 , [65] intersystem crossing is governed by many parameters such as column density and temperature.Their effects are difficult to predict because the exited state potential energy surfaces of varying isotopomers and corresponding vibrational/rotational energy distribution are impossible to accurately and precisely calculate at arequisite level. Therefore,e xisting studies were focused on the second and third absorption bands (i.e., photo-dissociation and photo-excitation bands,r espectively).…”

“…[60][61][62] As discussed, shielding requires that the isotopomers absorb at discrete wavelength. There are only three published experiments that have directly tested self-shielding.…”

Sulfur isotopic fractionation in vacuum UV photodissociation of hydrogen sulfide and its potential relevance to meteorite analysis

“…Accidental nearresonances between vibrational levels of different electronic states can significantly enhance radiationless transfer into the final dissociative state, and such resonances are responsible for the vibrational level-dependent predissociation. Isotope specificity caused by accidental predissociation has been observed in diatomic molecular systems, including N 2 and CO (25,44,45). Unlike diatomic molecules, where the potential energy surface is a function of bond length, for triatomic molecules, the added variable of bond angle further complicates the dissociation dynamics (36).…”

Photodissociation of CO isotopologues: Models of laboratory experiments and implications for the solar nebula

“…Laboratory experiments evaluating oxygen isotope fractionation during CO photolysis were carried out at the Advanced Light Source (ALS) synchrotron (Chakraborty et al. , ). The experiments were performed in a windowless, differentially pumped apparatus, with an approximately 1 meter photocell and a slow continuous flow of CO.…”

“…The photolysis experiments were carried out using the direct undulator beam (2.2 nm FWHM, photon flux approximately 5 × 10 14 ph s −1 from 91 to 110 nm) (Chakraborty et al. ). The beam entered a photocell of length approximately 100 cm, and containing CO at a column density of 1.3 × 10 17 –12 × 10 17 cm −2 .…”