l-doublet splittings in Δ vibrational state of 15N14N16O isotopomer

Abstract

We report the direct experimental evidences of l-doublet fine splittings between the parity doublet e and f sub-states of β-site isotopomer of nitrous oxide (15N14N16O) in the (1220)←(0220) ro-vibrational transition for l = 2 (i.e. Δ state) vibrational state in the mid-IR 7.8 µm spectral region. Due to extremely small splittings it remains a challenge for recording the fine structure doubling features for l = 2 or higher states. The existence of l-type doubling was investigated by high-resolution and ultra-sensitive cavity ring-down spectroscopy coupled with an external-cavity quantum cascade laser. We determined several new spectroscopic parameters such as l-type doubling constants, Coriolis constants, band centres, rotational constants and centrifugal distortion constants for l = 2 state of β-site N2O isotopomer by probing the rotationally resolved spectral lines with higher J values in the P-branch. Subsequently, the pressure broadening effect on the l-doublets and the corresponding broadening coefficients for both e and f sub-states in Δ state of β-site N2O were explored. Our high-resolution spectroscopic measurements will be useful for better fundamental understanding of linear polyatomic molecules and their isotopomers.

Keywords

• Cavity ring-down spectroscopy
• Quantum cascade laser
• Vibrational rotational spectra
• Nitrous oxide
• Doublets
• Doubling constant