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

A study at Ohio State University is probing the nature of a unique sulfur-containing molecule — one that scientists consider a “missing link” in its chemical family.

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.

Scientists 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 here to study the molecule in detail for the first time. Frank De Lucia, professor of physics at Ohio State, and his colleagues designed the instrument to utilize their FAST Scan Submillimeter Spectroscopy Technique (FASSST).

The technique offers a quick way for scientists to examine the spectrum of light given off 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 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 Jürgen Gauss at Johannes Gutenberg University in Mainz, Germany.

Behnke, now a postdoctoral researcher at Ohio State, explained that 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 detailed spectroscopic identification of HSOH using FASSST.

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.

The Ohio State physicists were able to create the molecule in a high-temperature chemical reaction — approximately 1100°C (2000°F), and used FASSST to image the spectrum.

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 Science Foundation funded this work.

#

Contact: Markus Behnke, (614) 292-1971; Behnke.14@osu.edu
Frank De Lucia, (614) 688-4774; Delucia.2@osu.edu

Written by Pam Frost Gorder, (614) 292-9475; Gorder.1@osu.edu