A pair potentials study of matrix-isolated atomic zinc. I. Excited 1P1 state dynamics in solid Ar

2000

J. Phys. Chem. A

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Luminescence in the vacuum UV/visible region has been recently recorded for atomic cadmium isolated in the rare gas solids Ne, Ar, Kr, and Xe, and because of the availability of diatomic Cd‚RG and RG‚RG pair potentials, theoretical calculations are now performed and compared to the recorded luminescence spectra. Calculations were first done for the gas-phase excited-state cluster species Cd( 1 P 1 )‚RG n , where n is the number of rare gas atoms in the cluster. The Cd‚RG 4 , Cd‚RG 5 , and Cd‚RG 6 clusters showed energy minima for the Cd p z orbital situated at the center of the planar rare gas clusters. With the rare gas distances in the planar clusters fixed at the rare gas dimer bond lengths, the cluster showing the greatest stabilization was the Cd‚ RG 5 species. The cluster calculations were then extended into the solid state for Cd occupying a single substitutional site of the solid rare gas lattice. Two vibronic modes lead to a preferential interaction between the guest and four rare gas atoms, thereby reducing the excited-state energy and leading to distinct minima. The modes are (a) the "body" mode (Q 2 ), which involves the motion of the Cd atom toward an octahedral interstitial site and (b) the "waist" mode (Q 3 ), which involves the in-phase contraction of four rare gas atoms in a single plane toward the Cd atom. Calculations based on single substitutional site occupancy of Cd in the rare gases indicate excited state stabilization for the waist mode for all hosts except neon. The body mode exhibits stabilization in Kr and Xe only. The pair of singlet emission bands observed in the Cd/Kr system is identified as originating from the stabilization of both vibronic modes in the excited state. The lack of stabilization for either mode in Ne, even though singlet emission exists in Cd/Ne, is indicative that a multivacancy site occupancy is likely here.

Section: Methodsmentioning

confidence: 99%

Simulation of Atomic Cadmium Spectroscopy in Rare Gas Solids Using Pair Potentials

Healy

2000

J. Phys. Chem. A

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“…Expressions similar to those listed above for the square planar Zn•RG 4 and square pyramid Zn•RG 5 cluster species listed above are used for the atoms in these categories. Further details are to be found in the preceding 14 and earlier publications. 1…”

Section: A Theoretical Simulationsmentioning

confidence: 99%

“…In the Zn•RG 5 systems, r is the distance of the rare-gas atom on the apex of the square pyramid to the base of the square pyramid, which is a constant, given the rigid cluster calculations done. As outlined in the preceding 14 and earlier articles, 1 the fourfold symmetry of the fcc rare-gas lattices allows the 18 rare-gas atoms considered in the Zn•RG 18 matrix calculations to be categorized into four groups. Expressions similar to those listed above for the square planar Zn•RG 4 and square pyramid Zn•RG 5 cluster species listed above are used for the atoms in these categories.…”

Section: A Theoretical Simulationsmentioning

confidence: 99%

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A pair potentials study of matrix-isolated atomic zinc. II. Intersystem crossing in rare-gas clusters and matrices

Breckenridge

Morse

The Journal of Chemical Physics

1998

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The mechanism of 4p 1 P 1 →4p 3 P J intersystem crossing ͑ISC͒ following excitation of the 4p 1 P 1 level of matrix-isolated atomic zinc is investigated using a pair potentials approach. This is achieved by extending earlier ISC calculations on the Zn•RG 2 and Zn•RG 3 complexes to the square planar Zn•RG 4 and square pyramidal Zn•RG 5 species which are the building blocks of the Zn•RG 18 cluster used to represent the isolation of atomic zinc in the substitutional site of a solid rare-gas host. ISC predictions in these clusters are based on whether crossing of the strongly bound 1 A 1 states, having a 4p 1 P 1 atomic asymptote, occurs with the repulsive 3 E states correlating with the 4p 3 P J atomic level of atomic zinc. Predictions based on 1 A 1 / 3 E curve crossings for 3 E states generated with the calculated ab initio points for the Zn•RG 3 ⌺(p z ) states do not agree with matrix observations. Based on similar overestimation of ISC in the Zn•RG diatomics, less repulsive Zn•RG 3 ⌺(p z ) potential curves are used resulting in excellent agreement between theory and observations in the Zn-RG matrix systems. 1 A 1 / 3 E curve crossings do not occur in the Zn-Ar system which shows only singlet emission. Curve crossings are found for the Zn-Xe system which exhibits only triplet emission. The Zn-Kr system does not show a crossing of the body mode Q 2 , which exhibits a strong singlet emission at 258 nm while the waist mode Q 3 , does have a crossing, resulting in a weak singlet emission at 239 nm and a stronger triplet emission at 312 nm. The efficiency of ISC is determined from Landau-Zener estimates of the surface hopping probabilities between the 1 A 1 and the 3 E states. Differences in the application of this theory in the gas and solid phase are highlighted, indicating that the rapid dissipation of the excited-state energy which occurs in the solid must be included to obtain agreement with observations.

“…The most obvious difference is that the emission in neon consists of just a single band while pairs of bands are present in the heavier rare gases. The existence of the pairs of emission bands has been attributed [30] to distinct relaxed excited state geometries originating from single vacancy site occupancy. The contrasting behaviour observed for atomic zinc in neon would suggest that the site occupied in this host is different to the other rare gases.…”

Section: Zn/rg Luminescencementioning

confidence: 99%

Metal atom (Zn, Cd and Mg) luminescence in solid neon

Healy

Kerins

Low Temperature Physics

2012

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Luminescence spectroscopy of the metal atoms Mg, Zn and Cd isolated in solid neon is recorded using pulsed synchrotron radiation excitation of the ns 1 np 1 1 P 1 -ns 2 1 S 0 resonance (n = 3, 4 and 5 respectively) transitions. Two features, a dominant band and a red-shoulder, are identified in the UV absorption spectra of Zn/Ne and Cd/Ne. Excitation of these features yields distinct emission bands with the red-shoulder absorption producing the smaller, Stokes-shifted emission. Nanosecond decaytime measurements, made with the time correlated single photon counting technique indicate the emission bands arise from the spin singlet 1 P 1 → 1 S 0 transition. Hence, it is concluded the duplication of absorption and emission features in the Cd/Ne and Zn/Ne systems arises from metal atom occupancy in two distinct sites. In contrast, Mg/Ne luminescence consists of single excitation and emission bands, indicative of occupancy in just one site. The occurrence of distinct photophysical characteristics of the linewidths, Stokes shift and lifetimes in the Mg/Ne system, compared with those recorded for Zn/Ne and Cd/Ne, is rationalised in terms of a different site occupancy for atomic Mg. Accurate interaction potentials for the ground states of the M·Ne diatomics are used to analyse site occupancies and interpret this contrasting behavior.