Ro–vibrational analysis of the first hexad of hydrogen sulfide: Line position and strength analysis of the 4ν₂ band of H₂³²S and H₂³⁴S for HITRAN applications

The high resolution infrared spectrum of hydrogen sulfide H₂³²S was recorded with a Bruker IFS 125HR Fourier transform infrared spectrometer and analyzed in the region of 4400–5400 cm⁻¹ where ro–vibrational bands of the so–called first hexad of hydrogen sulfide are located. The present study is focused on the weak 4ν₂ band. The 505 transitions with maximum values of the quantum numbers J^max=17 and K_a^max=8 (J^max = 9 and K_a^max=7 in the preceding studies) were assigned in the experimental spectrum. On this basis, 132 upper ro–vibrational energies (which is 2.5 times as high as in the preceding studies) were obtained. These data were used in the weighted fit of the Watson Hamiltonian parameters. The 28 varied parameters reproduce the 132 initial energy values with the root mean square deviation d_rms=3.5×10⁻⁴ cm⁻¹. Strength analysis of the 287 strongest experimentally recorded transitions was made by the fit of their line shapes with the Hartmann-Tran profile. The eight effective dipole moment parameters of the 4ν₂ band were obtained from the weighted fit which reproduce the initial experimental line strengths with the d_rms=3.1%. A comparison of the obtained results with the results of variational calculations and HITRAN data is presented. For the first time, transitions of the 4ν₂ band of H₂³⁴S were assigned in the experimental spectrum.