We discuss the formation of molecular oxygen in ultracold collisions between hydroxyl radicals and atomic oxygen. A time-independent quantum formalism based on hyperspherical coordinates is employed for the calculations. Elastic, inelastic and reactive cross sections as well as the vibrational and rotational populations of the product O{sub 2} molecules are reported. A J-shifting approximation is used to compute the rate coefficients. At temperatures T = 10--100 mK for which the OH molecules have been cooled and trapped experimentally, the elastic and reactive rate coefficients are of comparable magnitude, while at colder temperatures, T < 1 mK, the formation of molecular oxygen becomes the dominant pathway. The validity of a classical capture model to describe cold collisions of OH and O is also discussed. While very good agreement is found between classical and quantum results at T = 0.3 K, at higher temperatures, the quantum calculations predict a higher rate coefficient than the classical model, in agreement with experimental data for the O + OH reaction. The zero-temperature limiting value of the rate coefficient is predicted to be about 6 x 10{sup -12} cm{sup 3} s{sup 01}, a value comparable to that of barrierless alkali metal atom-dimer systems and about a factor of five larger than that of the tunneling dominated F + H{sub 2} reaction.We discuss the formation of molecular oxygen in ultracold collisions between hydroxyl radicals and atomic oxygen. A time-independent quantum formalism based on hyperspherical coordinates is employed for the calculations. Elastic, inelastic and reactive cross sections as well as the vibrational and rotational populations of the product O{sub 2} molecules are reported. A J-shifting approximation is used to compute the rate coefficients. At temperatures T = 10--100 mK for which the OH molecules have been cooled and trapped experimentally, the elastic and reactive rate coefficients are of comparable magnitude, while at colder temperatures, T < 1 mK, the formation of molecular oxygen becomes the dominant pathway. The validity of a classical capture model to describe cold collisions of OH and O is also discussed. While very good agreement is found between classical and quantum results at T = 0.3 K, at higher temperatures, the quantum calculations predict a higher rate coefficient than the classical model, in agreement with experimental data for the O + OH reaction. The zero-temperature limiting value of the rate coefficient is predicted to be about 6 x 10{sup -12} cm{sup 3} s{sup 01}, a value comparable to that of barrierless alkali metal atom-dimer systems and about a factor of five larger than that of the tunneling dominated F + H{sub 2} reaction.

Feb 1, 20240 citations

Formation of molecular oxygen in ultracold O+OH collisions

Goulven Quéméner, N. Balakrishnan, Brian K. Kendrick

We discuss the formation of molecular oxygen in ultracold collisions between hydroxyl radicals and atomic oxygen. A time-independent quantum formalism based on hyperspherical coordinates is employed for the calculations. Elastic, inelastic, and reactive cross sections as well as the vibrational and rotational populations of the product ${\mathrm{O}}_{2}$ molecules are reported. A $J$ -shifting approximation is used to compute the rate coefficients. At temperatures $T=10--100\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ for which the OH molecules have been cooled and trapped experimentally, the elastic and reactive rate coefficients are of comparable magnitude, while at colder temperatures, $T<1\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ , the formation of molecular oxygen becomes the dominant pathway. The validity of a classical capture model to describe cold collisions of OH and O is also discussed. While very good agreement is found between classical and quantum results at $T=0.3\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ , at higher temperatures, the quantum calculations predict a larger rate coefficient than the classical model, in agreement with experimental data for the $\mathrm{O}+\mathrm{O}\mathrm{H}$ reaction. The zero-temperature limiting value of the rate coefficient is predicted to be about $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.2em}{0ex}}{\text{molecule}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, a value comparable to that of barrierless alkali-metal atom-dimer systems and about a factor of five larger than that of the tunneling dominated $\mathrm{F}+{\mathrm{H}}_{2}$ reaction.We discuss the formation of molecular oxygen in ultracold collisions between hydroxyl radicals and atomic oxygen. A time-independent quantum formalism based on hyperspherical coordinates is employed for the calculations. Elastic, inelastic, and reactive cross sections as well as the vibrational and rotational populations of the product ${\mathrm{O}}_{2}$ molecules are reported. A $J$-shifting approximation is used to compute the rate coefficients. At temperatures $T=10--100\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ for which the OH molecules have been cooled and trapped experimentally, the elastic and reactive rate coefficients are of comparable magnitude, while at colder temperatures, $T<1\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$, the formation of molecular oxygen becomes the dominant pathway. The validity of a classical capture model to describe cold collisions of OH and O is also discussed. While very good agreement is found between classical and quantum results at $T=0.3\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, at higher temperatures, the quantum calculations predict a larger rate coefficient than the classical model, in agreement with experimental data for the $\mathrm{O}+\mathrm{O}\mathrm{H}$ reaction. The zero-temperature limiting value of the rate coefficient is predicted to be about $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.2em}{0ex}}{\text{molecule}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, a value comparable to that of barrierless alkali-metal atom-dimer systems and about a factor of five larger than that of the tunneling dominated $\mathrm{F}+{\mathrm{H}}_{2}$ reaction.

arXiv:0811.4377Physical Review AFeb 5, 200933 citations

{\mathrm{O}}_{2}

molecules are reported. A

J

-shifting approximation is used to compute the rate coefficients. At temperatures

T=10--100\phantom{\rule{0.3em}{0ex}}\mathrm{mK}

for which the OH molecules have been cooled and trapped experimentally, the elastic and reactive rate coefficients are of comparable magnitude, while at colder temperatures,

T<1\phantom{\rule{0.3em}{0ex}}\mathrm{mK}

, the formation of molecular oxygen becomes the dominant pathway. The validity of a classical capture model to describe cold collisions of OH and O is also discussed. While very good agreement is found between classical and quantum results at

T=0.3\phantom{\rule{0.3em}{0ex}}\mathrm{K}

, at higher temperatures, the quantum calculations predict a larger rate coefficient than the classical model, in agreement with experimental data for the

\mathrm{O}+\mathrm{O}\mathrm{H}

reaction. The zero-temperature limiting value of the rate coefficient is predicted to be about $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.2em}{0ex}}{\text{molecule}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, a value comparable to that of barrierless alkali-metal atom-dimer systems and about a factor of five larger than that of the tunneling dominated

\mathrm{F}+{\mathrm{H}}_{2}

reaction.