Pure rotational spectroscopy of sodium chloride, NaCl, up to 930 GHz

Abstract

The pure rotational spectra of both isotopomers of NaCl, i.e. 23Na35Cl and 23Na37Cl, have been recorded in high resolution with the Cologne terahertz spectrometer. A total of 189 new rotational lines have been measured in the frequency region between 200 and 930 GHz. Twenty nine of these transitions are assigned for Na35Cl to the vibrational ground state with J ≤ 72, and 102 lines arise from vibrationally excited states up to the 5th vibrational state: v = 5. For Na37Cl a total of 58 rotational lines with J ≤ 76 and v ≤ 4 could be detected. The newly measured lines were fitted together with the published microwave and millimeter-wave transitions to obtain a refined and extended set of molecular parameters: Na35Cl: B0 = 6513.04908(41) MHz, D0 = 9.338978(141) kHz, H0 = -1.0433(144) mHz and Na37Cl: B0 = 6373.74158(66) MHz, D0 = 8.943327(185) kHz, H0 = -0.9623(162) mHz. From the experimental data the equilibrium constants Be, α, γ, De, β, δ, He and ε are calculated as well. The refined parameters for both isotopomers allow precise frequency predictions to be made far into the terahertz region. Thus this new and highly precise data set for NaCl is intended to support future astrophysical observations.