Rovibrational quenching calculations of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow><mml:msub><mml:mi mathvariant="normal">C</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow><mml:mo>−</mml:mo></mml:msup></mml:math> in

The molecular anion <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msup><a:mrow><a:msub><a:mi mathvariant="normal">C</a:mi><a:mn>2</a:mn></a:msub></a:mrow><a:mo>−</a:mo></a:msup></a:math> has been of interest in the past few years as a candidate for laser cooling due to its electronic structure and favorable branching ratios to the ground electronic and vibrational states. Molecular hydrogen has been used by the Wester group at Innsbruck as a buffer gas to cool the molecule's internal rovibrational motion. In the present work we generate a five-dimensional (5D) interaction potential for the system by considering the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:msub><c:mi mathvariant="normal">H</c:mi><c:mn>2</c:mn></c:msub></c:math> as a rigid rotor and the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:msup><e:mrow><e:msub><e:mi mathvariant="normal">C</e:mi><e:mn>2</e:mn></e:msub></e:mrow><e:mo>−</e:mo></e:msup></e:math> as a rotating-vibrating diatomic molecule. We then calculate the cross sections and rate coefficients for rovibrational inelastic collisions of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:msup><g:mrow><g:msub><g:mi mathvariant="normal">C</g:mi><g:mn>2</g:mn></g:msub></g:mrow><g:mo>−</g:mo></g:msup></g:math> with both para- and ortho-<i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:msub><i:mi mathvariant="normal">H</i:mi><i:mn>2</i:mn></i:msub></i:math> on this 5D potential energy surface using quantum scattering theory for the dynamics. The rates for vibrational quenching are obtained over a range of temperatures that covers the single point measured by the experiments. A comparison is also made with earlier results which had used a simpler 3D interaction potential. Para-<k:math xmlns:k="http://www.w3.org/1998/Math/MathML"><k:msub><k:mi mathvariant="normal">H</k:mi><k:mn>2</k:mn></k:msub></k:math> is found to be more efficient than ortho-<m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:msub><m:mi mathvariant="normal">H</m:mi><m:mn>2</m:mn></m:msub></m:math> (with or without also undergoing rotational excitation) in cooling <o:math xmlns:o="http://www.w3.org/1998/Math/MathML"><o:msup><o:mrow><o:msub><o:mi mathvariant="normal">C</o:mi><o:mn>2</o:mn></o:msub></o:mrow><o:mo>−</o:mo></o:msup></o:math>. The rate coefficients for cooling the anions have been computed by appropriately weighting the ortho- and para-<q:math xmlns:q="http://www.w3.org/1998/Math/MathML"><q:msub><q:mi mathvariant="normal">H</q:mi><q:mn>2</q:mn></q:msub></q:math> and compared with the available experimental result at 20 K. The computed results are nearly two orders of magnitude larger than the single experimental point. When the vibrational deexcitation rate coefficients are employed without any concurrent rotational excitations in the final <s:math xmlns:s="http://www.w3.org/1998/Math/MathML"><s:msup><s:mrow><s:msub><s:mi mathvariant="normal">C</s:mi><s:mn>2</s:mn></s:msub></s:mrow><s:mo>−</s:mo></s:msup></s:math> anions (a situation considered to be nonphysical under the present experimental setup), the properly averaged results are found to get smaller and to become very close to the existing experimental measurements. The robustness of the present results is tested and confirmed. The implications of these results for laser cooling of <u:math xmlns:u="http://www.w3.org/1998/Math/MathML"><u:msup><u:mrow><u:msub><u:mi mathvariant="normal">C</u:mi><u:mn>2</u:mn></u:msub></u:mrow><u:mo>−</u:mo></u:msup></u:math> are analyzed and discussed.