Trace gas analysis with laser dispersion spectroscopy.

Trace gas analysis provides a wide range of insights into environmental processes, particularly with regards to global warming and air quality. With the urgent need to identify sources and accurately measure the harmful emissions negatively impacting our planet, Laser Dispersion Spectroscopy (LDS) offers a unique approach. LDS technology measures optical molecular dispersion via a differential phase measurement of light and, operating in the mid-infrared, provides highly sensitive and robust measurements. This enables highly precise, real-time gas measurements even in adverse environmental conditions such as rain, fog, snow or dust. The technology can be used in both extractive and open-path formats, with real-world applications including emissions monitoring on oil and gas sites, measuring the impact of agricultural activities and monitoring carbon capture storage facilities.

A variationally computed room temperature line list for AsH3.

Calculations are reported on the rotation-vibration energy levels of the arsine molecule with associated transition intensities. A potential energy surface (PES) obtained from ab initio electronic structure calculations is refined to experimental data, and the resulting energy levels display sub-wavenumber accuracy for all reliably known J = 0 term values under 6500 cm-1. After a small empirical adjustment of the band centres, our calculated (J = 1-6) rovibrational states reproduce 578 experimentally derived energies with a root-mean-square error of 0.122 cm-1. Absolute line intensities are computed using the refined PES and a new dipole moment surface (DMS) for transitions between states with energies up to 10 500 cm-1 and rotational quantum number J = 30. The computed DMS reproduces experimental line intensities to within 10% uncertainty for the ν1 and ν3 bands. Furthermore, our calculated absorption cross-sections display good agreement with the main absorption features recorded in the Pacific Northwest National Laboratory (PNNL) for the complete range of 600-6500 cm-1.