EricDuranzaArticleSummary

Article Title: Matrix Trapping Site for H Atoms in Solid Ne and Ar Authors: Stefano Ossicini and Frank Forstman DOI: http://dx.doi.org/10.1016/0301-0104(82)88032-4

1. Introduction
 * The species of interested are isolated by condensing them along a cold plate along with a matrix of an inert gas.
 * The crystalline of the matrix gas used allows for trapping sites of the target species at three separate spots: the substitutional site, the octahedral interstitial site and the tetrahedral interstitial site.
 * Previous work shows that H atoms are trapped at the substitutional and octahedral interstitial sites.
 * The sites at which atoms are trapped in largely depend on the initial state of the atom and in how the trapping is achieved.
 * Depositing H atoms from the gas phase achieves one trapping site while photolysis of H­2 already in the condensed phase yields several others.
 * These different methods to attain trapping also yield different internuclear distances of the H atoms.
 * In Ne matrices, trapping was only achieved by photolysis of H2.
 * Trapping of H atoms in an argon lattice causes an observed blue shift in the electronic transition energies.

2. The Model for the Matrix Influence
 * The outer electron of the target atoms in the matrix experience a perturbation potential, namely the Coulomb potential, of the atoms making up the matrix.
 * The target atoms also experience a repulsive potential due to its wavefunction needing to be orthogonal to the occupied states of the matrix atoms.
 * This change in the wavefunction is responsible for the shift in the electronic transition energies.

3. Results and Discussion
 * The measured values for the shifts in electronic transition energies for the 1s-2p in both Ne and Ar correspond most closely to the calculated value which suggests that the H atoms deposited in Ar and the H atoms of H2 photolysed in Ne are trapped at the substitutional position.
 * The rare gas lattice will relax around the target atoms built into it and the parameters regarding this relaxation are unknown.
 * Therefore, the calculations for determining the lattice sites for trapping are not exact numbers, but neighborhoods.

4. The Higher Transitions for H in Ne
 * When calculating the shift for the 1s-3p transition, the value was far off of the measured value.
 * This difference is explained by the quantum defect formula introduced in one of the listed sources (Resca et al. [13-15]).
 * Another source of theirs (Bohmer et al. [8]), uses a slightly different equation that is more appropriate when calculating the first excitation energy level where there is only a weak perturbation force acting on the atomic levels of the H atoms.
 * The first equation is used where it assumes that the electron orbitals are highly perturbed and is more suitable for the second and higher energy levels.
 * At even higher energy levels however, it does not matter as the quantum defect value does not vary all that much and becomes less important for larger excitation levels.

5. Conclusions
 * Based on the pseudopotential model developed previously for a trapped species and its matrix lattice, the shift of the absorption lines for the outer s electron was calculated.
 * The calculations made suggest that the site for deposited H atoms in an Ar matrix and for photolytic H atoms in a Ne matrix is the substitutional site and that it is possible for H atoms to be trapped at the octahedral position if the H atoms are produced by photolysis in an Ar matrix.
 * For impurities trapped in a Ne matrix, the excitations higher than the first are virtually the same and almost indistinguishable from excitons in Ne as they can be calculated using the exciton formula developed by Resca et al.