"Missing Link" Molecule May Offer Clues To Sulfur In Air, Space

The molecule, hydrogen thioperoxide, or HSOH for short, is related to the common bleaching and disinfectant agent hydrogen peroxide. Because HSOH contains sulfur, it could eventually help scientists understand how pollutants form in Earth's atmosphere, and how similar molecules form in outer space.

Researchers presented an initial study of the molecule June 18, 2002, at the annual International Symposium on Molecular Spectroscopy at Ohio State University.

A special laboratory instrument is allowing physicists to study the molecule and related species in much greater detail than ever before. This instrument, designed by Frank De Lucia, professor of physics at Ohio State, and his colleagues has been named the FAST Scan Submillimeter Spectroscopy Technique (FASSST) because of its capability to provide detailed spectral information in a very short time.

The technique offers a quick way for scientists to examine the spectrum of light absorbed by a molecule. Each molecule has its own one-of-a-kind spectral pattern. FASSST takes a snapshot of a wide range of spectral wavelengths, so scientists can easily recognize the pattern of the molecule they are looking for.

Since the 1960's, scientists have speculated that a sulfur molecule like HSOH could exist in Earth's upper atmosphere and outer space. Coal burning power plants, for instance, release sulfur from smokestack exhaust, and HSOH's other main ingredient -- water -- is abundant in the atmosphere.

But no one was able to synthesize the HSOH in the gas phase for investigations in the laboratory until Markus Behnke, a graduate student at the University of Cologne, Germany, did so in 2001. His collaborators on the HSOH synthesis project included Josef Hahn, Gisbert Winnewisser, and Sven Thorwirth at the University of Cologne, and JŸrgen Gauss at Johannes Gutenberg University in Mainz, Germany.

Behnke, now a postdoctoral researcher at Ohio State, explained why HSOH is considered a "missing link" molecule. With its mixture of hydrogen, oxygen, and sulfur, it exists somewhere between simple, sulfur-free molecules such as hydrogen peroxide and more complex molecules like sulfuric acid.

In his symposium presentation this week, Behnke reported the first synthesis and spectroscopic identification of HSOH in the gas phase.

The molecule was very difficult to study, because it exists only in extreme conditions: it is created during combustion at very high temperatures, but it breaks down unless it can be transferred quickly to an environment with very low temperature and pressure, such as the upper atmosphere. In addition, the chemical reaction that creates HSOH creates many other similar molecules at the same time.

Given those circumstances, synthesizing HSOH and recording its spectrum in the laboratory wasn't so much like looking for a needle in a haystack as "looking for an ant somewhere in Canada," Behnke said.

"Time-consuming calculations to predict the structure of HSOH led us finally to the first detection of this molecule and its relevant structural data," he continued. "The FASSST technique will be key to further investigations, when we look for other unknown molecules related to HSOH."

De Lucia observed that "the FASSST system is ideally suited for work of this type," and added that he is excited about applying the FASSST technique to future studies made possible by Behnke's synthesis of the molecule.

Scientists could one day use information about HSOH to better understand combustion, atmospheric pollution, and interstellar chemistry.

"This is very fundamental research," Behnke said, "but knowing the structure of simple molecules like HSOH could give us the foundation to understand more complex molecules later."

The National Aeronautical and Space Administration funds this work at Ohio State.