Boulter research group
Skye Doering, senior
Anna Volkert, graduated
Kirsten Strobush, graduated
Matt Hooper, graduated
My group’s current research activities are focused on laboratory investigations related to low-temperature chemistry of the terrestrial middle atmosphere and of extraterrestrial planetary atmospheres. Specifically, we are interested in their heterogeneous chemistry (chemical interactions that occur at the interface between atmospheric gases and particle surfaces) and their microscale morphology, or physical structure at size scales nearing the size of individual molecules. These ice particles typically form at temperatures below -150 degrees Celsius. Our research goals are to grow either pure or mixed ice films of various chemical compositions (including water, ammonia, hydrogen sulfide and methane). The films are grown in the laboratory under tightly controlled experimental conditions, and are then observed with various analytical tools (primarily infrared spectroscopy and mass spectrometry) as they are exposed to different gaseous chemical species in order to characterize the chemical interactions that occur at the surface. Because the nature of the surface morphology has a tremendous impact on heterogeneous reactivity, we also seek to understand the effect of composition and temperature on the size of pores, the degree of order or disorder (amorphous vs. crystalline), and how this affects measurable parameters such as density or surface area.
TERRESTRIAL UPPER-ATMOSPHERIC ICES
In Earth's middle atmosphere (between 60 and 90 km), particles are generally composed either of mineral materials resulting from meteors “burning up” as they enter the atmosphere or tiny water ice particles (often referred to as noctilucent clouds or polar mesospheric clouds) that form during the summertime near the poles at an altitude of about 83 km. In collaboration with investigators at SRI International in Menlo Park, CA, we are studying chemical reactions of atomic oxygen on the surface of these polar mesospheric clouds which may affect their formation, structure, and lifetime. One reason for our interest is that other investigators have suggested that either the frequency with which these clouds are observed or their brightness may be indicators of climate change in a region of the atmosphere which is less comprehensively studied. This research is funded by a grant from NASA Geospace Sciences. This work will help to support the scientific goals of the AIM (Aeronomy of Ice in the Mesosphere) satellite mission, which was launched in 2007. This research is supported by a grant from NASA Geospace Sciences.
EXTRATERRESTRIAL ATMOSPHERIC ICES
The visible disk of Jupiter is completely covered with clouds. However, its atmospheric composition leads to the formation of ammonia ice clouds, which are are formed as mixtures with other components such as water, hydrogen sulfide, and hydrocarbons. Possible species of upper-atmospheric ices include pure ammonia, ammonium hydrosulfide and various hydrates of those two. It has been suggested that complex hydrocarbon hazes may adsorb strongly to these particles, obscuring their spectral signature. In our lab, we utilize a high-vacuum chamber to deposit ice films of these chemical species in order to study their spectral signatures and other structural properties of the resulting mixed ices. These laboratory results may be compared to telescopic and remote observations and then assembled in computer models by other researchers to better understand the atmospheric chemistry and physics of these fascinating giant planets. Because these atmospheres are much less comprehensively observed and studied than our own, the application of techniques previously developed for studying the terrestrial atmosphere to new problems in extraterrestrial atmospheres should lead to significant advances. This research has been supported by a Research Corporation Cottrell College Science award.
OUR EXPERIMENTAL CAPABILITIES
These investigations are all performed in a high-vacuum chamber equipped with a single-stage CTI Helium cryostat, capable of generating temperatures as low as 30K. Ice films are grown on gold-plated mirror at the end of a machined copper coldfinger. To obtain ice films by indirect deposition, gas samples are introduced from a chilled glass ampoule or a glass bulb regulated using a leak valve. Directionally deposited films are grown from a differentially-pumped glass inlet terminating in a small orifice positioned opposite the mirror. Thin-film spectra are obtained using a Nicolet 730 FTIR spectrometer; the beam (polarized with a wire grid polarizer) is focused onto the mirror at a grazing angle of 85°. A HeNe laser is directed onto the substrate mirror at an angle of 35° to obtain interferometric film thickness measurements to determine film growth rates. The coldfinger is mounted on a vertical translation stage so that, in the upper position, the film is grown and infrared spectra and interferometric film thickness are measured. In the lower position, temperature-programmed desorption (TPD) mass spectrometric analysis is performed using a Hiden Analytical 3F/310 mass spectrometer, sampling through a 4.0 mm orifice. The mass spectrometer can also be used to measure background gas pressures during deposition.
Experimental vacuum chamber: top and side schematic views