A database of molecular spectra accurate to high temperatures and pressures

 

PI:        Scott T. Sanders, Assistant Professor, UW-Madison, ssanders@engr.wisc.edu

Engine Research Center, Department of Mechanical Engineering, UW-Madison

12 September 2006

 

Summary:

This whitepaper presents an aggressive program designed to revolutionize the understanding and implementation of gas molecular spectra, particularly at high temperatures and/or high pressures.

 

Members of the Engine Research Center plan to team with other experts (e.g., spectroscopic modelers) in this effort.  Contact Prof. Sanders if you are interested in joining the effort.

 

Plan:

• Measure gas absorption and emission spectra over a controlled range of temperatures and pressures in the Engine Research Center using recently developed test facilities.
  • Spectra will be highly resolved (< 0.1 cm^-1 resolution), and span a very broad range of wavelengths (200 – 20,000 nm). 
  • Temperatures to 3000 K
  • Pressures to 100 bar
  • Species targeted:
    • Any species of interest, provided room-temperature absorption features stronger than 1%/meter can be realized somewhere in the 200 – 20,000 nm range
    • The most popular candidates: OH, H₂O, CO₂
    • Other popular candidates: NO, CH₂O, O₂, hydrocarbons, CO
    • Countless species can be measured, but larger test matrices cost more to measure.  See budget section below.
  • The measurements are based on a new twist to traditional Fourier-transform spectroscopy concepts.
• Based on measured spectra, upgrade existing spectral models so that accurate spectra can be generated anywhere in the T = [300 .. 3000K], P = [1 .. 100 bar] range.
• Create a web-based tool that allows visitors to plot / download absorption and/or emission spectra (as well as corresponding spectra from databases such as HITRAN / HITEMP if desired)
  • In addition to spectra, fundamental information such as spectroscopic data and detailed spectral model functions will also be available from the web tool.

 

Spectral ‘appetizers’:

The below plots compare measured and simulated ν₁+ν₃ H₂O vapor spectra showing:

• Discrepancies in line positions and line strengths at high temperatures:

• Discrepancies in spectral broadening at high pressures and temperatures (note that the measured features are spectrally narrow compared to the simulated features):

 

Why is this database important?

• Spectral databases such as HITRAN, HITEMP, CDSD, LIFBASE, LIFSIM, and others (including, for example, other atmospheric databases) will be improved and/or supplanted.  At elevated temperatures and pressures, only a handful of gas spectra are treated in the above databases, and even in these cases, reliability is uncertain.  As the countless optical sensors based on such databases continue to evolve and become dedicated to applications, the fidelity of the databases becomes increasingly important.  More complete and more accurate databases are needed in many situations, including:
  • Improving the performance of existing optical diagnostics and sensors
  • Identifying new opportunities for optical diagnostics and sensors: e.g., detecting species with poorly-understood spectra or species in the presence of stronger interfering absorbers

Such applications span many fields including chemistry, astronomy, biology, physics, and engineering.

• Improving the understanding of molecular structure and other properties that are derived from fundamental spectroscopic data (thermodynamic properties, chemical properties, etc.)
• Ultimately such data and its application will lead to tangible progress including improved performance of energy-conversion and industrial processes, improved military systems, etc.

 

Approximate minimum budget:

Equipment (1000-20,000 nm range)	$120k
Additional equipment (200-1000 nm)	$50k
Experimental facility setup	$10k
Cost per species per octave in temperature; full pressure range, mostly personnel time	$10k
Cost per species; full temperature and pressure range, mostly personnel time	$33k
Total	$140k + $33k/species IR $190k + $33k/species UV-IR

 

For more information contact Prof. Sanders, ssanders@engr.wisc.edu