# Workshop on LABORATORY ASTROPHYSICS: Interstellar Gas, Dust and Ice

28-30 September 2016
Tagungstätte Schloss Ringberg, Kreuth
UTC timezone
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# Contribution Contributed Talk

Tagungstätte Schloss Ringberg, Kreuth -
AFTERNOON SESSION - GAS PHASE

# Experimental study of $\text{H}_2\text{D}^+$ and $\text{HD}_2^+$ recombination with electrons at low temperature. Laboratory astrophysics.

## Speakers

• Prof. Juraj GLOSIK

## Content

The recombination of deuterated trihydrogen cations $\rm H_3^+$ , $\rm H_2D^+$ , $\rm HD_2^+$ and $\rm D_3^+$ with electrons has been studied in stationary afterglow experiment with decaying plasma in $\rm He/Ar/ H_2 / D_2$ gas mixture. By monitoring the time evolutions of densities of all four cations during an afterglow as a function of $\rm H_2$ and $\rm D_2$ densities, using cavity ring down absorption spectrometer (SA-CRDS), we obtained the effective recombination rate coefficients for $\rm H_2D^+$ and $\rm HD_2^+$ ions for temperatures from 80 up to 140 K. From the measured dependencies of effective recombination rate coefficients on helium pressure the binary and ternary recombination rate coefficients for both ions have been determined. The inferred binary recombination rate coefficients are: $\rm \alpha_{bin}(H_2D^+,\ 80\ K) = (7.1 \pm 4.2)\times 10^{-8}\ cm^3s^{-1}$, $\rm \alpha_{bin}(HD_2^+,\ 80\ K) = (8.7 \pm 2.5)\times 10^{-8}\ cm^3s^{-1}$. The inferred rate coefficients of He assisted ternary recombination are: $K_{\rm H2D} (\rm 80\ K) = (1.1 \pm 0.6)\times 10^{-25}\ cm^6s^{-1}$ and $K_{\rm HD2}(\rm 80\ K) = (1.5 \pm 0.4)\times 10^{-25}\ cm^6s^{-1}$. Values of all four rate coefficients are similar to those of $\rm H_3^+$ and $\rm D_3^+$ at the same temperature [1,2]. Similarity with results obtained in previous studies of $\rm H_3^+$ and $\rm D_3^+$ recombination using SA-CRDS and FALP experiments supports our present results [3]. It is first time that recombination of $\rm H_2D^+$ and $\rm HD_2^+$ ions was studied in stationary afterglow experiment. Further studies over broader temperature and pressure ranges are in progress.

Acknowledgements This work was partly supported by Czech Science Foundation projects GACR 14-14649P, GACR 15-15077S, GACR P209/12/0233, and by Charles University in Prague Project Nr. GAUK 692214.

[1] P. Rubovic, P. Dohnal, M. Hejduk, R. Plasil, J. Glosik, Binary Recombination of H $_3^+$ and D $_3^+$ Ions with Electrons in Plasma at 50-230 K, J. Phys. Chem. A 117, 9626-9632, 2013

[2] R. Johnsen, P. Rubovic, P. Dohnal, M. Hejduk, R. Plasil, J. Glosik, Ternary Recombination of H $_3^+$ and D $_3^+$ with Electrons in He-H$_2$ (D$_2$) Plasmas at Temperatures from 50 to 300 K, J. Phys. Chem. A 117, 9477-9485, 2013

[3] M. Hejduk, P. Dohnal, P. Rubovic, A. Kalosi, R. Plasil, R. Johnsen, J. Glosik, Flowing-afterglow study of electron-ion recombination of para-H $_3^+$ and ortho-H $_3^+$ ions at temperatures from 60 K to 300 K, J. Chem. Phys. 143, 044303, 2015