Extended measurements and an experimental accuracy effective Hamiltonian model for the $3\nu_2$ and $\nu_4+\nu_2$ states of ammonia

Abstract

The infrared spectrum of ammonia has proven to be highly problematic for effective Hamiltonian analysis. The most complete previous study of the 3$\nu_2$ and $\nu_4+\nu_2$ bands achieved the accuracy of 0.0069 cm^-1 as reflected by the root-mean-square error of their fit, which is slightly more than 10 times the experimental accuracy. In the present study, we performed a global fit of the existing 2141 literature data involving $3\nu_2$, $\nu_4+\nu_2$, $3\nu_2-\nu_2$ , $(\nu_4+\nu_2)-\nu_2$ together with 1281 new data involving $3\nu_2-2\nu_2$, $3\nu_2-3\nu_2$ and $(\nu_4+\nu_2)-(\nu_4+\nu_2)$ using an effective Hamiltonian together with the Pickett suite of program SPFIT/SPCAT. The new dataset consists of three spectra recorded at the SOLEIL synchrotron facility. The effective Hamiltonian model proposed for $3\nu_2/\nu_4+\nu_2$ has achieved experimental accuracy. This success combined with our previous success of the $2\nu_2/\nu_4$ analysis leads us to believe that the vibrational states higher than $3\nu_2/\nu_2+\nu_4$ may be analyzed with effective Hamiltonians as well.

Olivier Pirali

Director of Research

My research interests includes high resolution molecular spectroscopy, laboratory astrophysics, and THz generation.