Chapter 3: Homework
Exercise:
Problems:
3.7 As shown in page 90 in the textbook, the ground state configuration of CO is
1σ22σ21π43σ2. A UPS detects the kinetic energy of an electron ejected from the
valence shell of the molecular orbitals. The electron configuration for the 1st excited
state of CO+ is 1σ22σ21π43σ1. The electron configuration for the 2nd excited state of
CO+ is 1σ22σ21π33σ2. The electron configuration for the 3rd excited state of CO+ is
1σ22σ11π43σ2. The splitting of peaks corresponding to the vibrational fine structure of
the excited states. When the electron was ejected from a strong bonding molecular
orbital, the resultant CO+ would have a weaker bond than that in original CO
molecule and vibrational fine structure would become clear. When the electron was
ejected from a non-bonding or weak bonding orbital, the resultant CO+ did not have
significant changes in bond length and vibrational fine structure was not clear. From
the UPS of CO, the 3σ MO has little contribution to C-O bond, while 1π MOs are
strong bonding orbitals. Similarly, 2σ MO does not contribute strongly to bonding.
The IEs of O, C, and S are 13.62, 11.26 and 10.36eV, respectively, the MO for SO
will be similar to that of CO, except the energy difference between S and O is greater
than that of C and O. Using similar MO energy diagram as that for CO, the ground
state configuration of SO is 1σ22σ21π43σ22π2. The 1st peak in the UPS of SO would
correspond to the 1st excited state of SO+ having the electron configuration of
1σ22σ21π43σ22π1. Since 2π's are antibonding orbitals, one should expect the bond
length to shrink after one electron was removed. The vibrational fine structure should
be seen because of the change in S-O bond length. The 2nd peak in the UPS of SO
would correspond to the 2nd excited state of SO+ having the electron configuration of
1σ22σ21π43σ12π2. Since 3σ is a weak bonding orbital, one should expect little or no
vibrational fine structure. The 3rd peak in the UPS of SO would correspnd to the 3rd
excited state of SO+ having the electron configuration of 1σ22σ21π33σ22π2. Since 1π's
are strong bonding orbitals, one should expect clear vibrational fine structure to be
seen.