Quantitative measurement of integrated band intensities of benzene vapor in the mid-infrared at 278, 298, and 323 K

Pressure broadened (1 atm. N₂) laboratory spectra of benzene vapor (in natural abundance) were recorded at 278, 298, and 323 K, covering 600-6500 cm⁻¹. The spectra were recorded at a resolution of 0.112 cm⁻¹ using a commercial Fourier transform spectrometer. The pressure of each benzene vapor sample was measured using high-precision capacitance manometers, and a minimum of nine sample pressures were recorded for each temperature. The samples were introduced into a temperature-stabilized static cell (19.94(1) cm pathlength) that was hard-mounted into the spectrometer. From these data a fit composite spectrum was calculated for each temperature. The number density for the three composite spectra was normalized to 296 K. The spectra give the absorption coefficient (cm² molecule⁻¹, naperian units) as a function of wavenumber. From these spectra integrated band intensities (cm molecule⁻¹ and atm⁻¹ cm⁻²) for intervals corresponding to the stronger benzene bands were calculated and were compared with previously reported values. We discuss and quantify error sources and estimate our systematic (NIST Type-B) errors to be 3% for the stronger bands. The measured absorption coefficients and integrated band intensities are useful for remote sensing applications such as measurements of planetary atmospheres and assessment of the environmental impact of terrestrial oil fire emissions.