H-atom diffusion through solid parahydrogen Robert Hinde, Dept. of Chemistry, Univ. of Tennessee

H-atom diffusion through solid parahydrogen Robert Hinde, Dept. of Chemistry, Univ. of Tennessee

H-atom diffusion through solid parahydrogen Robert Hinde, Dept. of Chemistry, Univ. of Tennessee

H-atom diffusion through solid parahydrogen Robert Hinde, Dept. of Chemistry, Univ. of Tennessee

H-atom diffusion through solid parahydrogen Robert Hinde, Dept. of Chemistry, Univ. of Tennessee

H-atom diffusion through solid parahydrogen Robert Hinde, Dept. of Chemistry, Univ. of Tennessee

H-atom diffusion through solid parahydrogen Robert Hinde, Dept. of Chemistry, Univ. of Tennessee Tunneling process is facile because the initial and final states are isoenergetic

Steering impurity-doped H-atom diffusion through solid parahydrogen Robert Hinde, Dept. of Chemistry, Univ. of Tennessee

Steering impurity-doped H-atom diffusion through solid parahydrogen Robert Hinde, Dept. of Chemistry, Univ. of Tennessee

Steering impurity-doped H-atom diffusion through solid parahydrogen Robert Hinde, Dept. of Chemistry, Univ. of Tennessee

Steering impurity-doped H-atom diffusion through solid parahydrogen Robert Hinde, Dept. of Chemistry, Univ. of Tennessee

Steering impurity-doped H-atom diffusion through solid parahydrogen Robert Hinde, Dept. of Chemistry, Univ. of Tennessee

Motivated by recent experiments of Mutunga et al. investigating HNNO formation in N 2 O-doped solid pH 2 : H atoms produced in situ via photolysis of precursor species in the matrix Mutunga et al., J. Chem. Phys. vol. 139, article (2013).

H atoms produced in situ via photolysis of precursor species in the matrix Mutunga et al., J. Chem. Phys. vol. 139, article (2013). What happens at different matrix temperatures?

Mutunga et al., J. Chem. Phys. vol. 139, article (2013). HNNO formation appears to “turn on” abruptly when the matrix temperature drops below T ≈ 2.4 K! Why? Trapping of H atoms in “pre-reactive” sites?

Figure by Anderson, based on Bradley et al., J. Chem. Phys. vol. 102, p (1995). Formation of HNNO proceeds via tunneling through an energetic barrier...

Figure by Anderson, based on Bradley et al., J. Chem. Phys. vol. 102, p (1995). Formation of HNNO proceeds via tunneling through an energetic barrier... preceded by a van der Waals complex: H NNO van der Waals complex

So we are interested in understanding the energetics of various H + N 2 O pre-reactive complexes, stabilized by the solid pH 2 matrix environment: N=N=O

So we are interested in understanding the energetics of various H + N 2 O pre-reactive complexes, stabilized by the solid pH 2 matrix environment:

Ar But first, let’s start with a simpler model system: Ar-doped solid pH 2...

A quantitative approach requires us to account for the constituents’ large-amplitude zero point motions: Simulations carried out using QSATS code: Hinde, Comput. Phys. Commun. vol. 182, p (2011). Ar H pH 2

Ar Evaluate the energies of various H Ar pairs, using “infinitely separated” H and Ar atoms as a reference:

Ar Evaluate the energies of various H Ar pairs, using “infinitely separated” H and Ar atoms as a reference:

Ar Evaluate the energies of various H Ar pairs, using “infinitely separated” H and Ar atoms as a reference:

SiteNominalRelative distance (a 0 )energy (K) 4 th NN ± rd NN ± nd NN ± 0.2 NN ± 1.3 ???

To understand these findings, let’s look at the pair interactions: Distance R (a 0 ) Ar–H pH 2 –H pH 2 –pH 2 Potential energy V(R) (K) Ar–pH 2

It’s highly unfavorable to displace a pH 2 molecule from the Ar dopant’s nearest-neighbor solvation shell! Distance R (a 0 ) Ar–pH 2 Ar–H pH 2 –H pH 2 –pH 2 Potential energy V(R) (K)

Take-home message: we can’t ignore the host matrix environment when evaluating the energies of the various H N 2 O pre-reactive complexes. N=N=O

Steering impurity-doped H-atom diffusion through solid parahydrogen Robert Hinde, Dept. of Chemistry, Univ. of Tennessee Thanks to: David Anderson group (U of Wyoming) NSF, UTK ($$$)