Dissociative electron recombination and rotational cooling of the deuterated triatomic hydrogen ions H 2 D + and D 2 H +

We have measured the dissociative recombination (DR) of the deuterated triatomic hydrogen ions <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:msub> <a:mi mathvariant="normal">H</a:mi> <a:mn>2</a:mn> </a:msub> <a:msup> <a:mrow> <a:mi mathvariant="normal">D</a:mi> </a:mrow> <a:mo>+</a:mo> </a:msup> </a:mrow> </a:math> and <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:msub> <d:mi mathvariant="normal">D</d:mi> <d:mn>2</d:mn> </d:msub> <d:msup> <d:mrow> <d:mi mathvariant="normal">H</d:mi> </d:mrow> <d:mo>+</d:mo> </d:msup> </d:mrow> </d:math> as a function of storage time at the Cryogenic Storage Ring (CSR). Both molecular ions were stored for up to 1000 s inside the cryogenic vacuum of the CSR prior to the electron recombination measurements, allowing them to cool to their lowest rotational states. We implement a comprehensive model for all relevant processes to predict the internal state evolution of the ions during storage inside the CSR, employing calculated radiative transition strengths and state-selective rate coefficients for electron collisions. Our DR rate coefficient measurements with deuterated triatomic hydrogen ions in defined quantum states allow for meaningful comparisons with state-of-the-art theoretical calculations, paving the way for a better understanding of the complex DR process for polyatomic molecular ions.