Thermal mobility of atomic hydrogen in solid argon and krypton matrices

The ͑NgHNg͒ + cations ͑Ng= Ar and Kr͒ produced via the photolysis of HF / Ar, HF / Kr, and HBr/ Kr solid mixtures are studied, with emphasis on their decay mechanisms. The present experiments provide a large variety of parameters connected to this decay phenomenon, which allows us to reconsider various models for the decay of the ͑NgHNg͒ + cations in noble-gas matrices. As a result, we propose that this phenomenon could be explained by the neutralization of the solvated protons by electrons. The mechanism of this neutralization reaction probably involves tunneling of an electron from an electronegative fragment or another trap to the ͑NgHNg͒ + cation. The proposed electron-tunneling mechanism should be considered as a possible alternative to the literature models based on tunneling-assisted or radiation-induced diffusion of protons in noble-gas solids. As a novel experimental observation of this work, the efficient formation of HArF molecules occurs at 8 K in a photolyzed HF / Ar matrix. It is probable that the low-temperature formation of HArF involves local tunneling of the H atom to the Ar-F center, which in turn supports the locality of HF photolysis in solid Ar. In this model, the decay of ͑ArHAr͒ + ions and the formation of HArF molecules observed at low temperatures are generally unconnected processes; however, the decaying ͑ArHAr͒ + ions may contribute to some extent to the formation of HArF molecules.

Section: B Low-temperature Formation Of Harfsupporting

confidence: 79%

Section: -4mentioning

confidence: 99%

See 1 more Smart Citation

Neutralization of solvated protons and formation of noble-gas hydride molecules: Matrix-isolation indications of tunneling mechanisms?

Khriachtchev

Lignell

Räsänen

2005

“…4 This temperature dependence fits well the mobility of atomic hydrogen in solid krypton lattice. 11 Both monomer and complex bands are thermally stable below the matrix sublimation temperature ͑ϳ40 K͒. The HKrCl¯N 2 bands are observed as intermediate during photolysis, qualitatively similar to the behavior of the monomeric HKrCl bands.…”

mentioning

confidence: 50%

Large blueshift of the H–Kr stretching frequency of HKrCl upon complexation with N2

Lignell

Khriachtchev

Pettersson

et al. 2002

Interaction between HKrCl and N 2 is investigated in a low temperature Kr matrix and by using ab initio calculations. Two configurations of the HKrCl¯N 2 complex are found both computationally and experimentally. The complexes show large monomer-to-complex blueshifts ͑ϩ112.9 and ϩ32.4 cm Ϫ1 experimentally͒ of the H-Kr stretching vibration mode. The large blueshifts are attributed to the enhanced ͑HKr͒ ϩ Cl Ϫ ion-pair character of complexed HKrCl resulting in stronger H-Kr covalent bonding.

“…The cage exit can happen either directly if there is enough momentum to climb over the potential barrier (created by the host atoms) or indirectly after cage deformations. Both exit and recombination mechanisms have been observed previously with hydrogen halides 1,2 in solid argon. In addition to the excess energy, the probability can be affected by controlling the vibrational and rotational initial state distributions.…”

Section: Introductionmentioning

confidence: 58%

Raman spectroscopy and crystal-field split rotational states of photoproducts CO and H2 after dissociation of formaldehyde in solid argon

Olbert‐Majkut

Pettersson

Kiljunen

2012

Self Cite

Kiljunen, T. (2012). Raman spectroscopy and crystal-field split rotational states of photoproducts CO and H2 after dissociation of formaldehyde in solid argon. The Journal of Chemical Physics, 137 (16), 164310-11. doi:10.1063 Raman signal is monitored after 248 nm photodissociation of formaldehyde in solid Ar at temperatures of 9-30 K. Rotational transitions J = 2 ← 0 for para-H 2 fragments and J = 3 ← 1 for ortho-H 2 are observed as sharp peaks at 347.2 cm −1 and 578.3 cm −1 , respectively, which both are accompanied by a broader shoulder band that shows a split structure. The rovibrational spectrum of CO fragments has transitions at 2136.5 cm −1 , 2138.3 cm −1 , 2139.9 cm −1 , and 2149 cm −1 . To explain the observations, we performed adiabatic rotational potential calculations to simulate the Raman spectrum. The simulations indicate that the splitting of rotational transitions is a site effect, where H 2 molecules can reside in a substitution site, in addition to an interstitial site. In the former site, rotational motion is unperturbed by the electrostatic field of the host atoms, while the latter site splits the excited rotational manifolds, J = 2 and 3, into doublet and triplet structures, respectively. For CO, the spectrum can be ascribed to monomeric species in single-and double-substitution sites, to a dimeric species (CO) 2 , and to a CO-H 2 O complex. The simulations show that a nearest-neighbor molecular complex CO-H 2 is not responsible for any of the observed spectral fingerprints. The cause of the exit of the molecular hydrogen from the initial cage can be traced to high translational energy of the fragment after the photodissociation. After the matrix has reached a thermal equilibrium, a diffusion driven formation of the complex is possibly hindered by the high rotational zero-point energy developed upon complexation.