High-accuracy sinewave-scanned direct absorption spectroscopy.

Area of Science:

• Spectroscopy
• Analytical Chemistry
• Physical Chemistry

Background:

• Direct absorption spectroscopy (DAS) is a common technique for gas analysis.
• Conventional DAS methods face challenges in accurate baseline determination and wavelength calibration.
• Accurate spectral data is crucial for understanding molecular interactions and atmospheric composition.

Purpose of the Study:

• To introduce a novel, highly accurate, and easily implemented sinewave-scanned direct absorption spectroscopy (DAS) method.
• To develop a time-domain fitting routine for simultaneous baseline and absorbance deduction.
• To improve upon conventional DAS by addressing baseline determination and wavelength calibration issues.

Main Methods:

• Developed a sinewave-scanned DAS technique.
• Implemented a time-domain fitting routine utilizing an explicit baseline expression.
• Experimentally verified the method using a CO transition at 4300.699 cm⁻¹.

Main Results:

• The novel DAS method achieved high accuracy and easy implementation.
• Simultaneous deduction of baseline and absorbance was successfully achieved.
• Accurate wavelength calibration was demonstrated, outperforming conventional DAS.
• Inferred CO line strength agreed well with HITRAN 2016 database.
• Provided more accurate N₂ collisional broadening data and reported speed-dependent coefficients for the first time.

Conclusions:

• The sinewave-scanned DAS method offers a significant advancement in spectroscopic analysis.
• This technique provides a robust solution for baseline determination and enhances measurement accuracy.
• The findings contribute valuable spectral data for CO, including precise collisional broadening parameters.