bonding

Question 1

what does empty state adsorbate interaction with sp-electrons result in?

Answer 1

the affinity (lowest unoccupied) level to drop and broaden out into an adsorbate band

Question 2

describe the adsorbate partially filled 1s (He) interaction with sp e-

Answer 2

1) the energy of the 1s orbital decreases following the surface barrier energy
2) no broadening of DOS as it is so tightly bound
3) the energy of the He + metal surface increases bc the He is repelled by the surface
4) the e- of the metal are strongly pushed away by the He, gives drop in charge density near the He
5) charge accumulates underneath and costs a lot of E
6) = repulsion between filled electronic levels

Question 3

describe the adsorbate filled 1s (H2) interaction with sp e-

Answer 3

1sigma_g shows broadening due to band formation as it approaches the surface

the energy of the orbital still decreases so the total molecule+surface energy increases bc the interaction is between filled states

shows a chemical interaction unlike He

Question 4

why does He not have a chemical interaction?

Answer 4

no broadening of the band, just simply going down in energy in DOS

Question 5

describe the adsorbate filled interactions of CO with sp e-

Answer 5

5sigma and 2pi* both decrease in energy and broaden as in H2 due to the background positive charge of the metal

Question 6

describe the bonding of adsorbates with d bands (TM metals)

Answer 6

1) moving across the TM series the d e- go down in energy as they get more filled
2) once the d and adsorbate level are the same in energy = covalent bonding, closer in energy = stronger bonding

Question 7

why do we want the d-band to only just be above the Fermi level for good bonding?

Answer 7

too low below Ef = not effective in bonding, too high above Ef = too reactive and holds to the adsorbate too tightly (like in He)

Question 8

what determines the amount of chemical bonidng?

Answer 8

the splitting