High-resolution cw-cavity ring-down spectroscopy of allowed (ν4 + ν5)0 and forbidden (ν4 + ν5)2 bands of C2H2 using external-cavity quantum cascade laser

Abstract

In this paper, we measured the absolute line intensities and air broadening coefficients of several rotationally resolved lines in the P and R branches of the allowed (ν4 + ν5)0 and forbidden (ν4 + ν5)2 vibrational combinational bands of C2H2 at room temperature 296 K. These measurements were performed using an external-cavity quantum cascade laser (EC-QCL) operating at 7.5 μm coupled with high-sensitive cavity ring-down spectroscopy (CRDS). Rotational level-dependent pressure-broadening coefficients of the resolved spectral lines of the selected transitions from (ν4 + ν5)0 band are reported here. The air broadening coefficients for 5 rotational lines from P-branch of (ν4 + ν5)2 band were also obtained first time with better than 3% uncertainty. The vibrational transition dipole moment squared values of the rotational lines and empirical Herman-Wallis coefficients were also quantified from experimental data. Finally, experimentally obtained all spectroscopic parameters were rigorously compared with previous studies. The new experimental data including several spectroscopic parameters will be useful for atmospheric and astrophysics applications.