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An absorption spectrum close to a core-level ionization threshold. Polarization-dependent core-to-unoccupied-state transitions probe orbital orientation and adsorbate geometry.

The large resonance at the smallest field-to-normal angle identifies an unoccupied orbital whose transition dipole is mainly normal to the surface. An N 1s initial state is approximately spherical; the dipole matrix element for a $1s\to {\pi }^{\ast }$ transition is directed along the normal to the adsorbate's aromatic plane. Consequently the adsorbate rings lie predominantly parallel to the copper surface. For perfectly flat molecules the resonance strength scales as $|\mathbf{E}\cdot \hat{\mathbf{n}}{|}^2\propto {\cos }^2\theta$, which decreases strongly from $17^{\circ }$ to $67^{\circ }$ as observed.

For azimuthally disordered molecular normals tilted by $\alpha$ from the surface normal, averaging gives $I(\theta )\propto {\cos }^2\theta {\cos }^2\alpha +\frac{1}{2}{\sin }^2\theta {\sin }^2\alpha$. Strong dichroism therefore implies a large orientational order parameter, but the plotted qualitative curves alone do not determine a unique tilt angle or distribution. Background subtraction, incident polarization and intensity normalization would be needed for such a fit. This experiment identifies the orientation of the pi system; it does not by itself identify a particular nitrogen–copper bonding topology.

The initial nitrogen environment loses intensity on heating, and a lower-binding-energy component becomes prominent near the highest temperatures. A change of surface chemical species accompanies loss or conversion of the original adsorbate. Plausible processes include thermally activated decomposition with nitrogen-containing fragments remaining on copper, desorption of intact material or fragments, and rearrangement of the coordination environment. The extra components at intermediate temperatures suggest coexistence rather than a rigid, uniform shift of every molecule.

The individual curves have vertical offsets, so their baseline height is not a coverage measurement. Integrated, sensitivity-corrected N and C peak areas, a clean heated substrate control, and evolved-gas mass spectrometry would help distinguish loss of material from chemical conversion. binding energy alone cannot establish a unique fragment structure: local charge, metallic screening and coordination all affect it.

The same wave vectors now differ in energy by only 0.070 eV, so the curvature is $A^{\prime }=0.14A=3.64756\mathrm{eV}{\mathring{\mathrm{A}}}^2$. ThereforeThe nearly free-electron in-plane mass and high unoccupied energy suggest an image-potential-derived state, with an electron confined outside the film by its image attraction and surface barrier but relatively free parallel to it. Relative to the supplied clean-platinum vacuum level, its minimum is 0.84 eV below vacuum, a plausible scale for an image state. gold adsorption can change the work function, so 0.84 eV is conditional on using the supplied clean-surface value; an adsorbate work-function measurement is needed for a quantitative assignment. The dispersion alone supports the interpretation without proving it uniquely.

When $|eV|$ reaches a vibrational quantum, a tunnelling electron can lose energy by exciting that vibration. Opening an inelastic channel changes $dI/dV$ at both voltage polarities. If the conductance increases in each direction, $d^{2}I/d{V}^2$ has a positive feature at positive threshold and a negative feature at the corresponding negative threshold. Approximate antisymmetry follows from approximate symmetry of the conductance; unequal tip and sample electronic structures can make amplitudes unequal.

The three energy scales are 8, 48 and 375 meV, corresponding to about 65, 387 and 3025 cm${}^{-1}$. A plausible assignment is a low-energy frustrated lateral translation or rotation, an adsorbate–metal stretch or hindered molecular mode at 48 meV, and a C–H stretching vibration at 375 meV. The terminal carbon of methyl isocyanide supplies a plausible adsorption contact, but exact mode assignment requires calculated normal modes or independent vibrational measurements. In particular the 48 meV band should not be labelled a C–N stretching vibration simply because the molecule contains that bond: its frequency is far too low for the usual internal stretching mode.