Theory of vibrational equilibria and pooling at solid-diatom interfaces

Abstract

In the present paper we provide a statistical theory for the vibrational pooling and fluorescence time dependence observed in infrared laser excitation of CO on an NaCl surface. The pooling is seen in experiment and in computer simulations. In the theory, we assume a rapid equilibration of the quanta in the substrate and minimize the free energy subject to the constraint at any time t of a fixed number of vibrational quanta N(t). At low incident intensity, the distribution is limited to one-quantum exchanges with the solid and the Debye frequency of the solid plays a key role in limiting the range of this one-quantum domain. The resulting inverted vibrational equilibrium population depends only on fundamental parameters of the oscillator (ω e and ω e χ e ) and the surface (ω D and T). The relation to the Treanor gas phase treatment is discussed. Unlike the solid phase system, the gas phase system has no Debye-constraining maximum. © 2013 AIP Publishing LLC. [http://dx

On the infrared fluorescence of monolayer 13CO:NaCl(100)

“…We confirm that for the monolayer, the overtone fluorescence results primarily from n = 8 to 10, as previously calculated. 6,7 We also confirm in the computations the theoretically predicted distribution function derived in another work, 8 as in Fig. 5.…”

“…We have described in a previous paper, 8 constraint on n does not hold for the CLIO excitation at short times, as in Fig. 3, but by 1 ms the assumption appears to hold reasonably well for both lasing conditions, as in Fig.…”

“…Importantly, the calculation supports the constrained vibrational population distribution recently derived theoretically for monolayers of high-frequency vibrations at solid surfaces where the assumptions of the model hold. 8 Further theoretical characterization of this high fluence regime, where the previous theoretical assumptions fail, is the topic of a forthcoming work. 16 The following experimentally testable predictions are also made:…”

“…Additionally, we test our previous theoretical prediction of the explicit form of the constrained vibrational population distribution function. 8 In it, the n-domain of a pool is restricted by the maximum energy that can be dissipated by pooling exchanges exciting only single-phonons in the solid.…”

Potential Energy Landscape of CO Adsorbates on NaCl(100) and Implications in Isomerization of Vibrationally Excited CO

“…[5][6][7][8][9] At high temperatures, the CO monolayer (ML) on NaCl(100) has a two-dimensional 1×1 lattice with CO oriented perpendicular to the surface, while this structure transforms to a 2×1 lattice with titled CO at temperatures lower than 35 K. [10][11][12] In a series of pioneering papers about thirty years ago, Chang and Ewing demonstrated that laser excitation of CO molecules adsorbed on cold NaCl(100) surfaces to their low-lying vibrational states (v=1) can lead to facile energy transfer among the adsorbates, resulting in some highly excited CO molecules, which can be detected from their spontaneous emission. [13][14][15] This so-called vibrational energy pooling has since attracted much attention from both theoretical [16][17][18][19] and experimental fronts. 20,21 The underlying basis for the CO molecules to climb the vibrational ladder is its anharmonicity, which gives rise to a small exoergicity for processes such as CO(v) + CO(v′) → CO(v-1) + CO(v′+1).…”