On the Pressure and Temperature Dependence of the Absorption Coefficient of NH₃

Abstract

The effects of pressure and temperature on the absorption coefficient of ammonia (NH3) gas self-perturbed and perturbed by nitrogen (N2) gas have been measured. We varied the gas pressure from 10 to 160 Torr and the temperature from 235 to 296 K in order to study the absorption coefficient at the center and the wings of lines in the ν4 band of NH3. These measurements were made using a high resolution (0.0038 cm-1) Bruker Fourier-transform spectrometer. These spectra have been analyzed using the method of multipressure technique permitting to succeed to an evolution of the absorption coefficient with the pressure and the quantum numbers J and K of the NH3 molecule. The results show that the absorption coefficient varies as a quadratic function of the pressure at the center of a given line. However, it has a linear evolution in the wings of the line. Moreover, the absorption coefficients are inversely proportional to temperature in the wings when NH3 lines are broadened by N2. The retrieved values of these coefficients were used to derive the temperature dependence of N2 broadening NH3 lines. The absorption coefficients were shown to fit closely the well-known exponential law.

Improved Sensitivity of Natural Gas Infrared Measurements Using a Filling Gas

“…The broadening effects are different for each band and also vary from the center of the band to its sides. 19 They were more dramatic at the C−H bending region (ca. 1600−1200 cm −1 ), where the bands at 1250 and 1350 cm −1 doubled their absorbance.…”

Measurement of automobile N2O from bag and continuous stream by quantum cascade laser spectroscopy

“…The target concentration of N 2 O in the bag was decided to be 400 and 600 ppb depending on the trend of N 2 O emission from most recent LDVs. 18,19 Concentration of CO and CO 2 were kept within 100–300 ppm and 1%–2%, respectively, also based on co-existence of these components in the real exhaust gas. Different concentrations of N 2 O, CO, and CO 2 were achieved by blending these three span gases with nitrogen at different ratios.…”

“…Therefore, at elevated temperature, gas absorbs more of lights and less light is transmitted. [18][19][20] With fewer transmitted lights, it becomes difficult to measure low concentration of gas as the signal to noise increases.…”

“…Individual absorption pulse widths are sensitive to intermolecular collisions and become broader with increasing pressure. [18][19][20] Therefore, total absorption across a band per mole of absorber increases with the gas pressure. A broader spectrum has higher risks of interference by the co-existing gases.…”

“…On the other hand, at high temperature, the transmittance becomes low due to higher kinetic energy of the gas molecules. [18][19][20] Based on experience, the cell pressure is selected at a significant vacuum of 0.25 atm and moderate gas temperature of 50°C in this study. A PID control loop is used to keep the cell and sample line temperature constant.…”