Enlarged molecules from excited atoms in nanochannels

The resonance interaction that takes place in planar nanochannels between pairs of excited-state atoms is explored. We consider interactions in channels of silica, zinc oxide, and gold. The nanosized channels induce a dramatically different interaction from that in free space. Illustrative calculations for two lithium and cesium atoms demonstrate that there is a short-range repulsion followed by long-range attraction. The binding energy is strongest near the surfaces. The size of the enlarged molecule is biggest at the center of the cavity and increases with channel width. Since the interaction is generic, we predict that enlarged molecules are formed in porous structures, and that the molecule size depends on the size of the nanochannels.

Figure 1

Full interaction energy between two lithium atoms [when the modes in the ($\pm$; $x$) branch are excited] and various limiting results as functions of separation, $\rho$. The full result from Eq. (9) is shown as the thick solid curve with circles; the large separation asymptote from Eq. (10) is represented by a thin curve with vertical bars; the $T=0$ K version of this asymptote from Eq. (11) is represented by the steepest of the two dotted straight lines; the other dotted line is the $n=0$ term from Eq. (12); the nonretarded full result is given by the solid straight line. All results are in atomic units (i.e., the energies in Hartree units and the separation in Bohr radii).

Figure 2

Full interaction energy between two symmetrically excited lithium atoms and between two symmetrically excited cesium atoms at the center of a 1 nm planar channel in silica.

Figure 3

Contribution from each term $n$ for the system shown in Fig. 2 for a case when the total interaction energy is repulsive ($\rho =20a_0$). The frequency decomposition of the interaction energy from $T_{xx}^1$, $T_{yy}^1$, $T_{zz}^1$ contributions and from the sum of these surface corrections, $U_{xx}^1$, $U_{yy}^1$, $U_{zz}^1$, and $U_{\mathrm{wall}}^1=U_{xx}^1+U_{yy}^1+U_{zz}^1$, respectively, is shown. Also shown is the total interaction energy contribution, $U_{\mathrm{total}}^1$, including both surface corrections and the free-space result from different frequencies. The discrete frequencies are shown at the top and at the bottom as circles. Note that for illustrative purposes the zero frequency contribution has been moved to the vertical axis.

Figure 4

Same as Fig. 3 but for a larger separation ($\rho =40a_0$) between the lithium atoms so that the total interaction energy is attractive.

Figure 5

Full interaction energy between two symmetrically excited lithium atoms in a 1 nm planar channel in silica (dashed curves), in zinc oxide (solid curves), and in gold (dotted curves). Here the atoms are positioned at the distance $z$ from one of the walls.

Figure 6

Minus the full interaction energy between a pair of lithium atoms in a symmetrically excited final state between two gold surfaces distances $d=1\mathrm{nm}$ and $d=2\mathrm{nm}$ apart.