Frequency comb assisted ir measurements of H3+, H2D+ and D2H+ transitions

We present recent measurements of the fundamental transitions of H$_3^+$, H$_2$D$^+$ and D$_2$H$^+$\footnote{ P. Jusko, C. Konietzko, S. Schlemmer, O. Asvany, {\it J. Mol. Spec.} 319 (2016) 55} in a 4~K 22-pole trap\footnote{ O. Asvany, S. Brünken, L. Kluge, S. Schlemmer, {\it Appl. Phys. B} 114 (2014) 203} by action spectroscopic techniques. Either Laser Induced Inhibition of Cluster Growth (He attachment at T$\approx$4~K), endothermic reaction of H$_3^+$ with O$_2$, or deuterium exchange has been used as measurement scheme. We used a 3 $\mu$m optical parametric oscillator coupled to a frequency comb\footnote{ O. Asvany, J. Krieg, S. Schlemmer, {\it Rev. Sci. Instr.} 83 (2012) 093110} in order to achieve accuracy generally below 1 MHz. Five transitions of H$_3^+$, eleven of H$_2$D$^+$ and ten of D$_2$H$^+$ were recorder in our spectral range. We compare our H$_3^+$ results with two previous frequency comb assisted works\footnote{ J.N. Hodges, A.J. Perry, P.A. Jenkins, B.M. Siller, B.J. McCall, {\it J. Chem. Phys.} 139 (2013) 164201}\footnote{ H.-C. Chen, C.-Y. Hsiao, J.-L. Peng, T. Amano, J.-T. Shy, {\it Phys. Rev. Lett.} 109 (2012) 263002}. Moreover, accurate determination of the frequency allows us to predict pure rotational transitions for H$_2$D$^+$ and D$_2$H$^+$ in the THz range