Cavity ring-down spectroscopy of water vapor in the near-UV region.

Water vapor absorption in the near-ultraviolet region is essential to describe the energy budget of Earth, but little spectroscopic information is available since it is a challenging spectral region for both experimental and theoretical studies. A continuous-wave cavity ring-down spectroscopic experiment was built to record absorption lines of water vapor around 415 nm. With a minimum detectable absorption coefficient of 4×10^-10 cm^-1, 40 rovibrational transitions of H¹⁶₂O were observed in this work, and 27 of them were assigned to the (224), (205), (710), (304), (093), (125), and (531) vibrational bands. A comparison of line positions and intensities determined in this work to the most recent HITRAN database is presented. Water vapor absorption cross-sections near 415 nm were calculated based on our measurements, which vary between 1×10^-26 and 5×10^-26 cm²/molecule. These data will also significantly impact the spectroscopy detection of trace gas species in the near-UV region. [ABSTRACT FROM AUTHOR]