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


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.

Journal of Molecular Spectroscopy
Olivier Pirali
Olivier Pirali
Director of Research

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