Abstract

The origin of the water spin isomers observed under various physico-chemical conditions is of great interest, including that of H₂O molecules in the gas phase. Here, terahertz time-domain spectroscopy (THz-TDS) was used to study the humidity-dependent ortho-to-para (O/P) ratio of water vapor at room temperature. The relative contents of para and ortho molecules were obtained by fitting the absorption lines of water vapor showing the relationship between the spin isomer contents and humidity. Larger O/P ratios with values of 3.2 were observed at lower humidity (<20%) due to the stronger attractive forces of para molecules. The concentration of the ortho isomers then began to decrease at higher humidity (>20%) due to the preferential formation of dimers and clusters at increasing concentrations. Thus, the ratio gradually decreased with increasing humidity.

© 2018 The Author(s)

Terahertz time-domain spectroscopy of water vapor

Martin van Exter, Ch. Fattinger, and D. Grischkowsky
Opt. Lett. 14(20) 1128-1130 (1989)

Isotope ¹⁸O/¹⁶O ratio measurements of water vapor by use of photoacoustic spectroscopy

Yutaka Matsumi, Masahiro Kishigami, Noriyuki Tanaka, Masahiro Kawasaki, and Gen Inoue
Appl. Opt. 37(27) 6558-6562 (1998)

Numerical method based on transfer function for eliminating water vapor noise from terahertz spectra

Y. Huang, P. Sun, Z. Zhang, and C. Jin
Appl. Opt. 56(20) 5698-5704 (2017)

Temperature determination of superheated water vapor by rotational-vibrational Raman spectroscopy

Leo A. Bahr, Peter Fendt, Yin Pang, Jürgen Karl, Thomas Hammer, Andreas S. Braeuer, and Stefan Will
Opt. Lett. 43(18) 4477-4480 (2018)

Suppression of spectral interferences due to water-vapor rotational transitions in terahertz time-domain spectroscopy

Yingxin Wang, Ziran Zhao, Zhiqiang Chen, Yan Zhang, Li Zhang, and Kejun Kang
Opt. Lett. 33(12) 1354-1356 (2008)