## 4 Results and Discussion
### Literature Comparison  
Table 2 summarizes our results at 294 K, along with the literature values of the NO (1\(\leftarrow\) 0) R11.5 (\(\Omega\)3/2 and \(\Omega\)1/2) lines from various published papers [20; 28; 29; 30; 31]. Note that we did not convert the broadening coefficients to the same temperature (at 300 K) as those in the literature for this comparison. The tabulated broadening coefficients are also shown in Figure 8. The different buffer gas means a different atom/molecule, and a different molecule has different collision frequency, energy and efficiency, which lead to different collision effects, and therefore, different broadening behavior. From the measurement results, the Ar broadening coefficient is the smallest, and the largest is the CO\({}_{2}\) broadening coefficient. For  
Figure 6: (**a**) Measured NO absorption spectra (20-scan average) in He at pressures of 929.1 mbar and 294.3 mbar. Below is a comparison of the residual between measured and fitted data, which results in an SNR of about 200. (**b**) Measured He-induced pressure broadening of the NO absorption lines fitted with a linear model. Below is a display of the residual between fit and data. NO-CO\({}_{2}\) and NO-H\({}_{2}\) broadening coefficients, there are no available reference data to compare. To the best of our knowledge, these two coefficients have not been reported before. \begin{table}
\begin{tabular}{c c c} \hline  & **R11.5 \(\Omega\)3/2** & **R11.5 \(\Omega\)1/2** \\ \hline \(\gamma_{\text{CO2}}\) [10\({}^{3}\) cm\({}^{-1}\)/atm] & 79.99 \(\pm\) 0.44 & 72.92 \(\pm\) 0.52 \\ Pressure range [atm] & 0.1–0.7 & 0.1–0.7 \\ Relative error [\%] & 0.55\% & 0.71\% \\ \hline \(\gamma_{\text{N2}}\) [10\({}^{3}\) cm\({}^{-1}\)/atm] & 58.13 \(\pm\) 0.31 & 50.8 \(\pm\) 0.27 \\ Pressure range [atm] & 0.1–0.9 & 0.1–0.9 \\ Relative error [\%] & 0.53\% & 0.53\% \\ Ref. [28] & 57.16(40) & 54.57(54) \\ Ref. [29] & 61.4(8) & 58.1(9) \\ \hline \(\gamma_{\text{Ar}}\) [10\({}^{3}\) cm\({}^{-1}\)/atm] & 42.64 \(\pm\) 0.22 & 37.67 \(\pm\) 0.19 \\ Pressure range [atm] & 0.1–1.0 & 0.1–1.0 \\ Relative error [\%] & 0.52\% & 0.50\% \\ Ref. [20] & 47.88(1.5) & 49.4(1.5) \\ \(\gamma_{\text{O2}}\) [10\({}^{3}\) cm\({}^{-1}\)/atm] & 57.68 \(\pm\) 0.66 & 50.88 \(\pm\) 0.53 \\ Pressure range [atm] & 0.1–0.3 & 0.1–0.4 \\ Relative error [\%] & 1.14\% & 1.04\% \\ Ref. [30] & 49.00(30) & 47.50(67) \\ \hline \(\gamma_{\text{H2}}\) [10\({}^{3}\) cm\({}^{-1}\)/atm] & 71.67 \(\pm\) 0.43 & 62.77 \(\pm\) 0.38 \\ Pressure range [atm] & 0.1–0.7 & 0.1–0.7 \\ Relative error [\%] & 0.60\% & 0.61\% \\ \hline \end{tabular}
\end{table} 
Table 2: Comparison of our findings with information from the literature regarding the NO (1\(\leftarrow\)–0) R (11.5) absorption lines’ broadening coefficients when combined with N\({}_{2}\), CO\({}_{2}\), Ar, H\({}_{2}\), O\({}_{2}\), He, and Air. Figure 7: (**a**) Measured NO absorption spectra (20-scan averaged) in H\({}_{2}\) at pressures of 671.4 mbar and 166.9 mbar. Below is a comparison of the residual between measured and fitted data, which results in an SNR of over 200. (**b**) Measured H\({}_{2}\)-induced pressure broadening of the NO absorption lines fitted linearly. Below is a display of the fit-to-data residual. N\({}_{2}\):O\({}_{2}\) = 79:21 is used to determine the NO-air broadening coefficient in Table 2 based on the measured NO-N\({}_{2}\) and NO-O\({}_{2}\) broadening coefficients. Peaks 1 and 2 have computed NO-Air broadening coefficients of 58.04(71) \(\times\) 10\({}^{-3}\) cm\({}^{-1}\)/atm and 50.82(63) \(\times\) 10\({}^{-3}\) cm\({}^{-1}\)/atm, respectively, at 294 K. Within the measurement uncertainty, the NO-air broadening coefficient determined by our study and based on our measured NO-O\({}_{2}\) and NO-N\({}_{2}\) values agrees well with HITRAN and Ref. [31]. The relative difference to [30] for the O\({}_{2}\)-induced pressure broadening coefficient is 15% for R11.5 \(\Omega\)3/2 and 6.7% for R11.5 \(\Omega\)1/2, while the measured temperatures in this reference were 299 K, 5 K higher than our result.