3 Search Results

A suppressed-Doppler (Δν = 180 MHz) infrared spectrum of monodeuterated ammonium ions (NH₃D⁺) has been obtained for the ν₁ (symmetric) and ν₄ (degenerate) N–H stretch bands via direct absorption high resolution IR laser spectroscopy in a planar slit jet discharge expansion. The ion is efficiently generated by H₃⁺ protonation of NH₂D in a discharge mixture of H₂/NH₂D, with the resulting expansion rapidly cooling the molecular ions into low rotational states. The first high-resolution infrared spectrum of ν₁ is reported, as well as many previously unobserved transitions in the ν₄ rovibrational manifold. Simultaneous observation of both ν₁ and ν₄ permits elucidationmore » of both the vibrational ground and excited state properties of the ion, including rigorous benchmarking of band origins against high-level anharmonic ab initio theory as well as determination of the ν₁:ν₄ intensity ratio for comparison with bond-dipole model predictions. Ground-state combination differences from this work and earlier studies permit the rotational constants of NH₃D⁺ to be determined to unprecedented accuracy, the results of which support previous laboratory and astronomical assignment of the 1₀–0₀ pure rotational transition and should aid future searches for other rotational transitions as well.« less

High-resolution rotationally resolved spectra of the N–H stretch vibrational mode (ν1) of jet-cooled ND₃H⁺ ions are collected and analyzed in a sub-Doppler slit-jet infrared spectrometer. The isotopomeric ammonium ions are generated by proton transfer from H₃⁺ to ND₃ in a discharge of an ND₃/H₂ gas mixture, whereby the slit jet expansion cools the nascent ND₃H⁺ ions into lower rotational states. Rotational assignments are confirmed by four-line combination differences that agree to within the spectrometer precision (9 MHz). Based on precision two-line ground-state combination differences and a symmetric top Hamiltonian, the B, D_J, and D_JK rotational constants for the ground vibrationalmore » state of ND₃H⁺ are determined with high precision for the first time. Approximate rotational constants for the ν₁ excited state are also determined, with a band origin at 3316.8425(19) cm^-1 and in remarkable (~0.1 cm^-1) agreement with high level anharmonic theoretical predictions by Guo and co-workers [J. Phys. Chem. A, 120, 2185 (2016)]. Our results allow us to predict several low-J pure rotational transitions of ND₃H⁺, which we hope will support future studies of this important ion in laboratory and astronomical rotational spectroscopy.« less