Infrared profile of NH3 trapped in argon matrix

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Abstract
A detailed theoretical analysis of the spectral profile of the ν2 infrared band of NH3 trapped in an argon crystal is performed. The coupled external (rotation + lattice and molecule center of mass translation) and internal (vibration + inversion) motions of the doped crystal are studied after decomposing the total Hamiltonian into renormalized parts connected to pseudooptical states and to pseudobath states. The calculation of the optical states (vibration‐inversion‐rotation or inversion‐rotation states) allows the bar infrared and far infrared spectra to be built and fairly well compared to experimental data. This model can quantitatively explain the narrowing of the ν2 inversion doublet, the splitting of the more intense R(0) branch into two peaks and the high frequency structures connected to the splittings of the R(1) branch by both the inversion and the hindered rotation processes. The infrared profile is then determined by using a conventional cumulant expansion method. The calculated linewidths and additional lineshifts are in close agreement with recent high resolution experimental spectra.