## 3 Results and Discussion
### Comparison with Literature Values  
We summarize our results in Table 1 together with the literature values of the HCl (1\(\leftarrow\)0) P5 line from various published papers. The tabulated broadening coefficients were also shown in Figure 7, together with the relative difference to this study comparing foreign broadening coefficients. Note that the term uncertainty is interpreted very differently between different literature data and the definitions are not explained in some papers;  
Figure 5: (**a**) Measured O\({}_{2}\)-broadened HCl absorption spectra in O\({}_{2}\) at 101.3 mbar and the fitting residual; (**b**) Measured O\({}_{2}\) induced pressure broadening with a linear fitting model. The residual between fit and data is shown below. Figure 6: (**a**) Measured HCl absorption spectra in O\({}_{2}\) at 101.3 mbar and the fitting residual; (**b**) Measured O\({}_{2}\) induced pressure broadening with a linear fitting model. The residual between fit and data is shown below. thus, the uncertainty quoted from the literature data have only a limited comparability. The column (to the right) in Table 1 shows the scaled results at 296 K for both this work and the literature data using the P5 line temperature dependance coefficients: \(n_{\text{air}}\) = 0.46, \(n_{\text{CO2}}\) = 0.75 from HITRAN, while for the other three (\(n_{\text{N2}}\), \(n_{\text{O2}}\), \(n_{\text{Ar}}\)) the default value \(n\) = 0.5 were used. For HCl-CO\({}_{2}\) broadening coefficient, the relative difference of the value shown in Ref. [25] to this study is 2.4% as shown in Figure 7. However, our present study still agrees with the literature value within the measurement uncertainty but with improved uncertainty. The measured HCl-N\({}_{2}\) broadening coefficient shows a very good agreement with the literature value in Ref [26]. For the HCl-Ar broadening coefficient there is a significant deviation of about 12% compared to the measured results in Ref [27]. Possible reasons might be the different pressure range of the experiment, a high pressure range (10-50 bar) was used in their experiments, while in comparison with the calculated value in Ref [27], the deviation is 2.4%, which shows an agreement with our result within the measurement uncertainty. The \"room temperature\" mentioned in the publication was not specified, so it might not be 294 K.  
For the O\({}_{2}\) induced pressure broadening coefficient, the relative difference is 7.5% to Ref [28], and 3.2% to Ref [29] in which the uncertainty was not mentioned. While in those two references, the measurement temperature was 298 K, which was 4 K higher than our measurement. Additionally, the pressure ranges were higher than ours--2-11 atm in Ref [28], up to 5 atm in Ref [29]. The deviation of HCl-Air broadening coefficient is 1.8% between our result and Ref [26] with 1K temperature difference. Comparing with the measured value in Ref [28] (2-11 atm, 298 K), the deviation is about 5.2%. If using the HCl-N\({}_{2}\) broadening coefficient in Ref [30] and HCl-O\({}_{2}\) broadening coefficient in Ref [28], as those two broadening coefficients were measured by same authors, based on N\({}_{2}\):O\({}_{2}\) = 80:20 (as mentioned in Ref [28]) the calculated HCl-Air broadening coefficient at 298 K is 53.74 cm\({}^{-1}\)/atm which is about 2.6% relative difference to their measured result in Ref [28], while, in our study, the calculated HCl-Air broadening coefficient based our measured HCl-O\({}_{2}\) and HCl-N\({}_{2}\) results (N\({}_{2}\):O\({}_{2}\) = 80:20) is 55.64 \(\pm\) 0.30 cm\({}^{-1}\)/atm which agrees very well (0.7% deviation) with the measured value within the measurement uncertainty. The literature data for foreign broadening coefficients of HCl in Table 1 are conveniently divided into two groups according to experimental pressures, i.e., group I for low pressure (<1 atm) and group II for high pressure (1-12 atm).