Knowledge Bank

The near-infrared absorption spectrum of NH$3$ is an interesting opportunity for atmospheric {\it in-situ} measurements of this species using tuneable diode-lasers. For this purpose, accurate line positions and intensities are indispensable. In the past, several studies of the absorption spectrum of $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$NH$3$ in the near-infrared were carried out, using Fourier-transform$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$ and tuneable diode-laser spectroscopy.$\mathrm{<mrow\; data-mjx-texclass="ORD">2-4</mrow>}$ More recently, high-resolution diode-laser spectra of $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$NH$3$ were analyzed for the first time.$\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}$ The lines of $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$NH$3$ in this region are also useful for wavenumber calibration of absorption spectra obtained with tuneable lasers. In our group, we have recently investigated the possibility to detect atmospheric NH$3$ using photoacoustic laser spectroscopy in the 1.5 $\mu$m region, and observed several discrepancies between individual line positions and intensities observed in our and previous studies$\mathrm{<mrow\; data-mjx-texclass="ORD">1,4</mrow>}$, as already noticed by other groups.$\mathrm{<mrow\; data-mjx-texclass="ORD">2,5</mrow>}$ In order to solve this problem we have measured new absorption spectra of $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$NH$3$ (and also of $\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}$NH$3$) in the 6300-7500 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ region using a Bruker IFS 120-HR Fourier-transform spectrometer. The length of the absorption cell was 30 cm. The NH$3$ pressures employed were around 30 mbar, and the spectral resolution used was 0.02 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$, leading to linewidths (Full-Width at Half-Maximum) of about 0.03 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$. Based on these spectra, we have produced a list of individual line positions and line intensities at 296 K. Comparisons with the previous studies$\mathrm{<mrow\; data-mjx-texclass="ORD">1-5</mrow>}$ will be presented. }, {\bf 162}, 230-245 (1993).} }, {\bf 40}, 2031-2042 (2004).} }, {\bf 45}, 31-45 (2004).} }, {\bf 28}, 59-66 (2004).} }, in press (2006).}