High-resolution spectra recorded with Fourier transform spectrometers (FTS) have been analyzed to determine line positions and intensities for transitions in the 1←0 bands of ¹²C¹⁶O, ¹³C¹⁶O, ¹²C¹⁸O and ¹³C¹⁶O, and air-broadened half-width and shift coefficients, their temperature dependences, line mixing and speed dependence parameters were measured for ¹³C¹⁶O and ¹²C¹⁸O transitions. These parameters were retrieved from two multispectrum fittings (1940-2260 cm⁻¹) of a data set that included two room-temperature spectra of a natural sample of CO recorded with the Kitt Peak FTS and self- and air-broadened spectra (up to 626 Torr) of ¹³C-enriched and ¹⁸O-enriched CO samples between 150 K and room temperature recorded with the JPL Bruker IFS-125HR FTS. Sample cells with path lengths of about 0.5, 1.1, 4.3 and 20.4 cm were used, and all but the shortest cell were temperature controlled. The retrieved 1←0 band strengths of ¹²C¹⁶O, ¹²C¹⁸O and ¹³C¹⁸O are very close to the HITRAN2012L. S. Rothman et al.,JQSRT 130 (2013) 4-50.alues, but for ¹³C¹⁶O the band strength is  ∼ 4.5% larger than the HITRAN2012 value and 2.6% higher than the HITRAN2016I. E. Gordon et al.,JQSRT 203 (2016) 3-69.alue.Research described in this talk was performed at Connecticut College, the College of William and Mary, Langley Research Center and the Jet Propulsion Laboratory, California Institute of Technology, under contracts and cooperative agreements with NASA.html:<hr /><h3>Footnotes: L. S. Rothman et al.,JQSRT 130 (2013) 4-50.v I. E. Gordon et al.,JQSRT 203 (2016) 3-69.v Research described in this talk was performed at Connecticut College, the College of William and Mary, Langley Research Center and the Jet Propulsion Laboratory, California Institute of Technology, under contracts and cooperative agreements with NASA.

The line parameters of self- and air-broadened methane in the ν₁+ν₄ and ν₃+ν₄ bands are determined using a nonlinear least-squares multispectrum fitting technique. We have analyzed a set of 14 laboratory spectra of pure methane and lean mixtures of methane in air which were recorded using a high-resolution Fourier Transform Spectrometer (FTS) at the Jet Propulsion Laboratory, California, employing a coolable sample cell with optical path length 20.38 cm. The line parameters determined in this analysis include line positions, intensities, self- and air-broadened line widths and pressure-induced shifts along with their temperature dependences, assuming a Speed-Dependent Voigt Profile (SDVP). The line mixing coefficients are quantified via the off-diagonal relaxation matrix element formalism. The broadening and shift parameters show good agreement with literature values and spectroscopic database entries. The observed line positions and intensities also agree fairly well with theoretically calculated results and values found in the spectroscopic databases. Spectroscopic parameters are also determined for some transitions of the ν₂+2ν₄, 2ν₂+ν₄ and 3ν₄ bands of methane in the spectral range 4100-4300 cm⁻¹.Research described in this talk was performed at the College of William and Mary, Langley Research Center and the Jet Propulsion Laboratory, California Institute of Technology, under contracts and cooperative agreements with NASA.html:<hr /><h3>Footnotes: Research described in this talk was performed at the College of William and Mary, Langley Research Center and the Jet Propulsion Laboratory, California Institute of Technology, under contracts and cooperative agreements with NASA.

The Great Oxygenation Event (GOE), the introduction of O₂ into the Earth’s atmosphere approximately 2.4 billion years ago, is a critical signpost in the development of life on Earth. The vanishing of sulfur isotope anomalies, called Sulfur Mass-Independent Fractionation (S-MIF), in the rock record is thought to be correlated with oxygenation of the early atmosphere. However, the mechanism for the generation of S-MIF in an anoxic atmosphere is unknown. Here, I propose a mechanism that involves spectroscopic perturbations in the B-X UV band system of S₂. This proposal is based on a global deperturbation analysis done by Green and WesternM.E. Green, C.M. Western, A deperturbation analysis of the B ³Σ_u⁻ (v' = 0-6) and the B" ³Π_u (v' = 2-12) states of S₂, J. Chem. Phys. 104 (3) (1996) 848-864.M.E. Green, C.M. Western, Upper vibrational states of the B" ³Π_u state of ³²S₂, J. Chem. Soc., Faraday Trans. 93 (3) (1997) 365-372. and work that I presented previously at this conference in 2015 (MG12) and 2016 (MG08). Specifically, perturbations of the “bright” B state by a “dark” B” state cause some isotopologues to have longer average excited state lifetimes than others. I demonstrate a difference between the shorter-lifetime symmetric (e.g. ³²S-³²S) isotopologues of S2, for which nuclear permutation symmetry causes half of the rotational lines to be missing, and the longer-lifetime asymmetric isotopologues (e.g. ³³S-³²S). I also comment on general features of the B/B” system of S₂ that make it uniquely well-suited to generate a large MIF isotope effect.

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Footnotes:

M.E. Green, C.M. Western, A deperturbation analysis of the B ³Σ_u⁻ (v' = 0-6) and the B" ³Π_u (v' = 2-12) states of S₂, J. Chem. Phys. 104 (3) (1996) 848-864.

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Footnotes:

Here, I continue my discussion of Sulfur Mass Independent Fractionation (S-MIF) in the S₂ B-X UV band system, relevant to the geologic signature of the anoxic atmosphere that existed prior to the Great Oxygen Event 2.4 billion years ago. To test a possible mechanism for the isotope effect, I implement a steady state, master equation kinetic model for every bound rovibronic state in the B/B” system. This model incorporates both rotationally inelastic and electronically inelastic collisions. The output of the model suggests that such collisions have negligible impact on average excited state lifetimes, indicating that the isotope effect is primarily spectroscopic in nature. The steady state populations that are output from the deperturbation/master equation model are useful in identifying which bright/dark state crossings are most proficient at populating long lifetime states, and thereby generating an S-MIF signature. A major conclusion from this analysis is that only a small minority of level crossings have such a capability, and, consequently, these have a dominant influence on the isotope effect averaged over the total system.

The distributions of the three most abundant isotopologues of carbonyl sulfide (OCS, O¹³CS, and OC³⁴S) have been measured in the Earth's stratosphere by infrared remote sensing with the Atmospheric Chemistry Experiment (ACE) Fourier transform spectrometer. These satellite observations have provided a near-global picture of OCS isotopic fractionation. The ACE data indicate a different enrichment trend with altitude for the O¹³CS and OC³⁴S isotopologues. The seasonal variation of the isotopologue enrichment was also studied using the ACE data. The Whole Atmosphere Community Climate Model (WACCM) has been used to model OCS and its isotopologue distributions in the stratosphere.

It is estimated that ~50% of climatically relevant atmospheric aerosols arise from new particle formation (NPF), the process by which trace atmospheric gases such as sulfuric acid and ammonia cluster and grow. Amines are expected to enhance NPF, with greater enhancement from larger amines. Using cryogenic ion vibrational predissociation (CIVP) spectroscopy, we studied the structural evolution of clusters with up to 3 sulfuric acids. It is shown that substitution of amines for ammonia can induce structural rearrangement, which is driven by the ability of the alkylamines (MA, DMA, TMA) to form hydrogen bonds, and can lead to direct bisulfate-bisulfate hydrogen bonds. This direct interaction between formal anions indicates that hydrogen bonding can compete with Coulombic force in determining cluster structure. From these observations we have developed a model to predict when these arrangements may arise in ionic and neutral clusters with a variety of compositions. This structural motif is correlated with the fastest growing amines, and could play a role in the mechanism of NPF.

Sulfur compounds have been observed in a number of planetary atmospheres throughout our solar system. While our current understanding of sulfur chemistry explains much of what we observe in Earth’s atmosphere, several discrepancies between modeling and observations of the Venusian atmosphere show there are still problems in our fundamental understanding of sulfur chemistry. Recent work in the Vaida lab has shown that electronically excited sulfur dioxide is incredibly reactive with a wide range of molecules including saturated alkanes. Using Infrared spectroscopic techniques, we have undertake a study to measure the rate constants for the reaction of electronically excited sulfur dioxide with a series of alkanes ranging from methane to n-nonane. We will present on the effect of chain length on the reaction rate and the effect of branched and ringed structures of alkanes on reaction with electronically excited sulfur dioxide.

A new method to quantify reaction product ratios using high resolution microwave spectroscopy in a cryogenic buffer gas cell has been developed. We demonstrate its power with product ratio quantification in the ozonolysis of isoprene, , the most abundant, non-methane hydrocarbon emitted into the atmosphere by vegetation. Purified and isoprene were mixed for approximately 10 s under dilute (1.5-4% in argon) continuous flow conditions in an alumina tube held at 298 K and 5 Torr. Products exiting the tube were rapidly slowed and cooled within the buffer gas cell by collisions with cryogenic (4-7 K) He. High resolution chirped pulse microwave detection between 12 and 26 GHz was used to achieve isomer-specific product quantification with ppb sensitivity. r0pt Figure We determined a ratio of MACR to MVK of 2.1 ± 0.4 under 1:1 ozone to isoprene conditions and 2.1 ± 0.2 under 2:1 ozone to isoprene conditions, a finding which is consistent with previous experimental results. The potential to perform a complete branching ratio analysis is discussed using ¹³C isotopic substitution of isoprene. We also discuss the prospects for detecting the proposed Criegee intermediates in this reaction, methacrolein-oxide and methyl vinyl ketone-oxide, neither of which have ever been observed.