High–resolution re–investigation of the ν 2 and ν 4 bending bands of phosphine (PH 3 )

Highlights: • Line positions are measured for the lowest bending dyad of PH${}_3.$ • Effective parameters of the bending dyad of PH${}_3$ are determined. • List of 6771 transitions is presented. High resolution infrared spectra of PH${}_3$ were recorded with a Bruker IFS125 HR Fourier transform infrared spectrometer at an optical resolution of 0.0025 cm${}^{-1}$ and analyzed in the region of 600–1700 cm${}^{-1}$ where the ${\nu }_2/{\nu }_4$ bending dyad is located. The number of 2207 and 4564 transitions (in general, 3099 "allowed" and 3672 "forbidden", which is about 2.5 times higher in comparison with the preceding studies) with $J^{\text{max}}$ = 29, $K^{\text{max}}$ = 28 ($J^{\text{max}}$ = $K^{\text{max}}$ = 24 in the earlier studies) were assigned to these two bands. Ground state parameters were improved on the basis of MW and IR data, known from the literature, and new IR data from the present study. The $A_1/A_2$ splittings for the states with the quantum number $K=13$ were experimentally recorded and theoretically explained for the first time. The weighted fit of 1284 upper energy values obtained from the experimentally recorded transitions was made with a Hamiltonian which takes into account resonance interaction between the $(0100,A_1)$ and $(0001,E)$ vibrational states. As the result, a set of 86 fitted parameters was obtained which reproduces the initial 1284 upper "experimental"ro–vibrational energy values with the $d_{\text{rms}}=9.8\times {10}^{-5}$ cm${}^{-1}$.