Subpromille Measurements and Calculations of CO (3-0) Overtone Line Intensities.

Intensities of lines in the near-infrared second overtone band (3-0) of ^{12}C^{16}O are measured and calculated to an unprecedented degree of precision and accuracy. Agreement between theory and experiment to better than 1‰ is demonstrated by results from two laboratories involving two independent absorption- and dispersion-based cavity-enhanced techniques. Similarly, independent Fourier transform spectroscopy measurements of stronger lines in this band yield mutual agreement and consistency with theory at the 1‰ level.

Assessment of the precision, bias and numerical correlation of fitted parameters obtained by multi-spectrum fits of the Hartmann-Tran line profile to simulated absorption spectra.

Although the Voigt profile has long been used to analyze absorption spectra, the quest for increased precision, accuracy and generality drives the application of advanced models of atomic and molecular line shapes. To this end, the Hartmann-Tran profile is now recommended as a standard for high-resolution spectroscopy because it parameterizes relevant higher-order physical effects, is computationally efficient, and reduces to other widely used profiles as limiting cases. This work explores the uncertainty with which line shape parameters can be obtained from constrained multi-spectrum fits of spectra simulated with this standard profile, varying uncertainty levels in the spectrum detuning and absorption axes, and spanning a range of sampling density, pressure, and line shape parameter values.

Improvement of the spectroscopic parameters of the air- and self-broadened NO and CO lines for the HITRAN2020 database applications.

This paper outlines the major updates of the line-shape parameters that were performed for the nitrous oxide (NO) and carbon monoxide (CO) molecules listed in the HITRAN2020 database. We reviewed the collected measurements for the air- and self-broadened NO and CO spectra to determine proper values for the spectroscopic parameters. Careful comparisons of broadening parameters using the Voigt and speed-dependent Voigt line-shape profiles were performed among various published results for both NO and CO.

Air-broadening in near-infrared carbon dioxide line shapes: Quantifying contributions from , , and Ar.

We measured air broadening in the (30012) ← (00001) carbon dioxide () band up to using frequency-agile rapid scanning cavity ring-down spectroscopy. By using synthetic air samples with varying levels of nitrogen, oxygen, and argon, multi-spectrum fitting allowed for the collisional broadening terms of each major air component to be simultaneously determined in addition to advanced line shape parameters at atmospherically relevant mixing ratios. These values were compared to broadener-specific line shape parameters from the literature.

Near-infrared cavity ring-down spectroscopy measurements of nitrous oxide in the (4200)←(0000) and (5000)←(0000) bands.

Using frequency-agile rapid scanning cavity ring-down spectroscopy, we measured line intensities and line shape parameters of N O in air in the (4200)←(0000) and (5000)←(0000) bands near 1.6 m. The absorption spectra were modeled with multi-spectrum fits of Voigt and speed-dependent Voigt profiles.

Cavity ring-down spectroscopy of CO near = 2.06 μm: Accurate transition intensities for the Orbiting Carbon Observatory-2 (OCO-2) "strong band".

The = 2.06 μm absorption band of CO is widely used for the remote sensing of atmospheric carbon dioxide, making it relevant to many important top-down measurements of carbon flux. The forward models used in the retrieval algorithms employed in these measurements require increasingly accurate line intensity and line shape data from which absorption cross-sections can be computed.

Twenty-Five-Fold Reduction in Measurement Uncertainty for a Molecular Line Intensity.

To accurately attribute sources and sinks of molecules like CO_{2}, remote sensing missions require line intensities (S) with relative uncertainties u_{r}(S)<0.1%. However, discrepancies in S of ≈1% are common when comparing different experiments, thus limiting their potential impact.

Towards a taxonomy of topology for polynuclear aromatic hydrocarbons: linking electronic and molecular structure.

Trends linking the topological characteristics of polynuclear aromatic hydrocarbons (PAH) to their electronic properties are reported. TD-DFT electronic spectra computations, using the 6-31G* basis set and B3LYP exchange correlation functional, were calculated for a series of PAH, allowing for the HOMO-LUMO gaps to be reported. Clar structures provide an avenue to link the physical structure and the aromaticity of the molecule; which, when extended by bond length and harmonic oscillator model of aromaticity analysis, provide powerful tools to understand the link between electronic and physical structure.

Extinction measurements for optical band gap determination of soot in a series of nitrogen-diluted ethylene/air non-premixed flames.

Visible light extinction was measured in a series of nitrogen-diluted, ethylene/air, non-premixed flames and this data was used to determine the optical band gap, OBG, as a function of flame position. Collimated light from a supercontinuum source is telescopically expanded and refocused to match the f- number of a dispersing monochromator. The dispersed light is split into a power metering channel and a channel that is periscoped and focused into the flame.