Adsorption states of NO on the Pt(111) step surface

Abstract

Using infrared reflection absorption spectroscopy (IRAS) and scanning tunneling microscopy (STM), we investigated the adsorption states of NO on the Pt(997) step surface. At 90 K, we observed three N-O stretching modes at 1490 cm −1 , 1631 cm −1 and 1700 cm −1 at 0.2 ML. The 1490 cm −1 and 1700 cm −1 peaks were assigned to NO molecules at fcc-hollow and on-top sites of the terrace, respectively. The 1631 cm −1 peak was assigned to the step NO species. In the present STM results, we observed that NO molecules were adsorbed at the bridge sites of the step as well as fcc-hollow and on-top sites of the terrace. To help with our assignments, density functional theory calculations were also performed. The calculated results indicated that a bridge site of the step is the most stable adsorption site for NO, and its stretching frequency was 1607 cm −1 . The interactions between NO species at different sites on Pt(997) are also discussed.

Potential Energy Surface of NO on Pt(997): Adsorbed States and Surface Diffusion

“…Therefore, the stable adsorption site for NO molecules on the step edge is a twofold bridge site, and the peak at 1610 cm −1 is assigned to NO at the bridge site of the upper step (BS species). Compared to the previous DFT calculation, the BS species is the most stable species, and the stretching frequency is 1607 cm −1 , which is in good agreement with the experimental results [16]. The other peak at 1385 cm −1 , which appears at 11 K, is assigned to the NO at the HS species shown in Figure 4(b).…”

“…Therefore, the most stable adsorption site for NO is the BS site, and the 2nd and 3rd most stable sites are the HT and OT sites, respectively. These results are in good agreement with the previous DFT calculation [16] and are summarized in Table 1. and the coverage of OT, HT, and BS species as a function of elapsed time.…”

“…The other peak at 1385 cm −1 , which appears at 11 K, is assigned to the NO at the HS species shown in Figure 4(b). From the DFT calculation, there is a stable adsorption site at an HS (hcp) site as shown in Figure 4(b), and its calculated stretching frequency is 1188 cm −1 [16]. This is smaller than the experimental result.…”

“…The duration time (the open time of the valve) was in the order of ms (typically 2 ∼ 5 ms) and much shorter than the measurement time. Details of the experiments are described in our previous papers [15][16][17].…”

“…The stable adsorption site of CO on Pt(997) is only an on-top site at low coverage, and the activation barrier to CO hopping is about 190 meV [20][21][22]. On the other hand, the number of stable adsorption sites for NO is larger than for CO, and the activation barrier to NO hopping is higher than * The adsorption energy is the result from the previous DFT studies [10,16].…”