國家同步輻射研究中心
News
/
In Focus
water,
ortho
-to-
para
ratio, OPR, vacuum ultraviolet, VUV
The Collaborative Research of NSRRC Scientist Yu-Jong Wu and User Hui-Fen Chen Highlighted as a Cover of
Journal of Physical Chemistry Letters
2023/01/17
The collaborative research of Dr. Yu-Jong Wu and Prof. Hui-Fen Chen revealed that vacuum–UV irradiation of O
2
and H
2
adsorbed on a grain surface might be a plausible route for contributing to a smaller
ortho
-to-
para
ratio of interstellar H
2
O. The research was highlighted in a cover of
Journal of Physical Chemistry Letters
.
Water is an important species widely found in various astro-environments. It exists in two isomers with distinct total nuclear spin, namely
para
-H
2
O and
ortho
-H
2
O. Following spin statistics, the
ortho
-to-
para
ratio (OPR) of H
2
O is 3 at temperatures greater than 50 K. In the past 30 years, non-statistical OPR values of water have been obtained in various astro-enviroments, which were considered to convey the message of the thermal process under 30 K during its formation. However, recent experimental result revealed that the OPR of H
2
O desorbed from interstellar ices was 3 regardless of the formation temperature. Thus, the OPR of interstellar H
2
O smaller than 3 is an important yet unresolved subject in astrochemistry.
The research team led by the NSRRC Scientist, Dr. Yu-Jong Wu and NSRRC user, Prof. Hui-Fen Chen in Medicinal and Applied Chemistry of Kaohsiung Medical University worked in collaboration on this issue. They proposed a plausible route for explaining the observation of low OPR in space. Vacuum-UV light generated from TLS 21A2 was used to irradiate O
2
in solid H
2
which made the preferential formation of interstellar
para
-H
2
O via the reaction of O + H
2
. According to their experimental results, the H
2
O formed in this scheme can produce an OPR as small as ~1.6 upon photolysis. This paper has been featured on the inside cover of
Journal of Physical Chemistry Letters
.
J. Phys. Chem. Lett. 13, 10439 (2022)