W ater on the S un?

Researchers Confirm that Water Exists On The Sun Press Release no. 115 -- July 17, 1997

University of Waterloo

WATERLOO, Ont. -- An international team of scientists, including a University of Waterloo chemistry professor, has conclusively demonstrated that water (actually steam) does exist on the sun, confirming a breakthrough finding made two years ago.

The team used an innovative method to calculate the water spectrum at sunspot temperatures. The method will be useful in modelling systems with an abundance of extremely hot water molecules, such as forest fires.

The team was led by Oleg Polyansky, a theoretician from Russia's Institute of Applied Physics; Nizhnii Novgorod, who works with co-researcher Jonathan Tennyson, a physicist at University College, London; and UW chemistry Prof. Peter Bernath, an expert in molecular astronomy. Other team members included Serena Viti, a physicist at University College, London; Nikolai Zobov, a physicist at University College, London; and Lloyd Wallace, an astronomer at Kitt Peak National Observatory, Tucson, Ariz.

In their 1995 study, the team recorded evidence of water -- not in liquid form because the sun is too hot, but as vapor or steam -- in dark sunspots. The scientists compared the laboratory infrared spectrum of hot water with that of a sunspot.

The water in the sunspots causes a sort of "stellar greenhouse effect" that affects the sunspot's energy output. Hot water molecules are also the most important absorbers of infrared radiation in the atmospheres of cool stars, such as "variable red giants."

In their follow-up study, to be published today in the journal Science, the scientists examined the spectrum of extremely hot water such as that found in sunspots and in the laboratory. Hot water has a complicated infrared spectrum characterized by a dense series of sharp absorption lines.

But the transitions that give rise to those lines were not known, until now. The research team carried out a simulation of the infrared spectrum based purely on theoretical calculations, allowing accurate assignments of the absorption lines.

"The detailed interpretation of the infrared spectrum of hot water is one of the important unsolved problems in molecular spectroscopy," the researchers write in their Science article.

The spectroscopic data will be useful in modelling other systems that contain extremely hot water molecules, such as forest fires and rocket plumes. Spectral analysis captures the characteristic spectra, or wavelength patterns, emitted or absorbed by molecules.

"Our research team solved the problem by doing something completely different," Bernath said. "Starting with a mathematical model that is progressively improved through perturbation theory doesn't work for hot water."

Instead, the team went directly to theory and used the calculated interaction energies of the atoms of water. By using sophisticated variational calculations of energy levels, the researchers predicted the position of transitions that give rise to absorption lines.

"The calculations were so good that they were close enough to the observations for us to make sense of the spectrum," said Bernath, who led the team that carried out the laboratory spectroscopy. Spectroscopy is the study of the interaction of light and matter.

Contact: John Morris, UW News Bureau, (519) 888-4567, ext. 6047 Prof. Peter Bernath, (519) 888-4567, ext. 4814

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