# First accurate experimental study of Mu reactivity from a state-selected reactant in the gas phase: the Mu + H 2 1 reaction rate at 300 K

 Title First accurate experimental study of Mu reactivity from a state-selected reactant in the gas phase: the Mu + H 2 1 reaction rate at 300 K Publication Type Journal Article Year of Publication 2015 Authors Bakule, P, Sukhorukov, O, Ishida, K, Pratt, F, Fleming, D, MOMOSE, T, Matsuda, Y, Torikai, E Journal Journal of Physics B: Atomic, Molecular and Optical Physics Volume 48 Pagination 045204 Abstract This paper reports on the experimental background and methodology leading to recent results on the first accurate measurement of the reaction rate of the muonium (Mu) atom from a state-selected reactant in the gas phase: the Mu + H 2 ##IMG## [http://ej.iop.org/images/0953-4075/48/4/045204/jpb505072ieqn3.gif] {$\{1\}\to$} MuH + H reaction at 300 K, and its comparison with rigorous quantum rate theory, Bakule et al (2012 J. Phys. Chem. Lett. 3 [http://dx.doi.org/10.1021/jz3011496] 2755 ). Stimulated Raman pumping, induced by 532 nm light from the 2nd harmonic of a Nd:YAG laser, was used to produce H 2 in its first vibrational ( v = 1) state, H ##IMG## [http://ej.iop.org/images/0953-4075/48/4/045204/jpb505072ieqn4.gif] {$_{2}\{1\}$} , in a single Raman/reaction cell. A pulsed muon beam (from ‘ISIS’, at 50 Hz) matched the 25 Hz repetition rate of the laser, allowing data taking in equal ‘Laser-On/Laser-Off’ modes of operation. The signal to noise was improved by over an order of magnitude in comparison with an earlier proof-of-principle experiment. The success of the present experiment also relied on optimizing the overlap of the laser profile with the extended stopping distribution of the muon beam at 50 bar H 2 pressure, in which Monte Carlo simulations played a central role. The rate constant, found from the analysis of three separate measurements, which includes a correction for the loss of ##IMG## [http://ej.iop.org/images/0953-4075/48/4/045204/jpb505072ieqn5.gif] {${{\rm H}_{2}\{1\}$} concentration due to collisional relaxation with unpumped H 2 during the time of each measurement, is ##IMG## [http://ej.iop.org/images/0953-4075/48/4/045204/jpb505072ieqn6.gif] {${k}_{\rm Mu}}\{1\}$} = 9.9[(−1.4)(+1.7)] × 10 −13 cm 3 s −1 at 300 K. This is in good to excellent agreement with rigorous quantum rate calculations on the complete configuration interaction/Born–Huang surface, as reported earlier by Bakule et al , and which are also briefly commented on herein. URL http://stacks.iop.org/0953-4075/48/i=4/a=045204