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Published online: 17 December 2008 | doi:10.1038/nchina.2008.293

Interstellar chemistry: The state of hydroxide

Tim Reid

Introduction

© (2008) National Academy of Sciences

The humble hydroxide ion (OH^-) is one of the chemicals that can be identified in the immense void between stars. Scientists can learn a lot about the void by studying how water molecules are split into H⁺ and OH^- ions by ultraviolet light. The OH^- ions might emerge from this process in either rotational or vibrational states, according to research by Xueming Yang at the Chinese Academy of Sciences in Dalian, China, Richard Dixon at the University of Bristol, UK, and co-workers¹.

Previous studies have shown that water can absorb many different bands of ultraviolet to produce H⁺ and OH^- ions in a variety of rotational or vibrational states. However, these bands mainly refer to averages over a large group of molecules in several different states.

Yang and co-workers resolved individual states of water molecules using an ultraviolet laser with wavelengths shorter than 200 nm. This is called vacuum ultraviolet because it is readily absorbed by air, but can exist in space.

The researchers observed a variety of excited hydroxide ions — some with strong rotations but weak vibrations, and some with weak rotations and strong vibrations. This competition between rotation and vibration depends on the original state of the water molecule and the directions in which the H⁺ and OH^- ions are ejected.

The authors of this work are from:
State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China; School of Chemistry, University of Bristol, Bristol, UK.

Reference

1. Yuan, K. et al. Nonadiabatic dissociation dynamics in H₂O: Competition between rotationally and nonrotationally mediated pathways. Proc. Natl Acad. Sci. USA 105, 19148–19153 (2008).  | Article | PubMed | ChemPort |