课程名称︰物理化学二 课程性质︰化学系必修 课程教师︰陈振中 开课学院：理学院 开课系所︰化学系 考试日期（年月日）︰98.01.15 考试时限（分钟）：120 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : Section A (80%) 1. (20%) The Balmer Series has an equation of the following form: 1/λ = R [ 1 / 2^2 - 1 / n^2 ] The energy expression of the Bohr's model of a one-electron atom: En = -2.178*10^-18 Z^2 / n^2 (a) Derive the value of R in terms of the Planck's constant and light velocity. (b) What is the shortest wavelength of the emission spectrum of Be3+? 2. (20%) In a rather crude bonding model of the hydrogen molecular ion, H2 +, the electron may be considered as a particle in a one-dimentional box whose width is the same as the intermolecular separation r. Consider the ground state only in the following questions. The Bohr radius (hbar^2 * 4πε0 / m e^2 ) is equal to 0.53 angstrom; the H atom ground-state energy (- m e^4 / 8 h^2 ε0^2 ) is -13.6 eV. a. Express the kinetic energy T of the election as a function r. b. Assuming the average potential energy V of the electron to be that of an election at rest midway between the nuclei, express the total energy E as a function of r. c. Calculate the equilibrium bond distance r0 in angstrom and the ground-state energy E0 in eV. The experimentl values are 1.06 angstrom and -16.3 eV, respectively. [Hints: Your calculated ground state energy should be higher than the experimental value.] 3. (20%) Cyclobutadiene, C4H4, is a four-carbon ring. Write the secular equation for the π molecular orbitals of this planar molecule. Find the energies of the orbitals. Predict the total π electronic energy of this compound. Is these extra π electron stabilization (as butadiene or benzene ) in this molecule? 4. (20%) Consider the one-particle, one dimentional system with potential-energy V = V0 for l/4 < x < 3l/4, where V0 = hbar^2 / m l^2 V = 0 for 0 < x < l/4 and 3l/4 < x <l V = ∞ elsewhere Treat the system as a perturbed particle in a box. Find the first-order energy correction E^(1) for the energy eigenstate with quantum number n. Section B (20%) ＿ 1. (10%) Consider the trial function of ψ(x) = √30 x (a-x) / a^(5/2). Use the variational method to obtaion an upper bound to the ground-state energy of a particle in-a-line of length a and compare the result with the true value. 2. (10%) Consider a dimer formed by two monomers, viz. A and B. Assume that each of the monomers has two energy states only. The normalized ground states of the two monomers are designated as ψA0 and ψB0, whereas the normalized excited states are denoted as ψA1 and ψB1, respectively. That is, we have ^ ^ H ψ = E ψ and H ψ = E ψ A A0 0 A0 B B0 0 B0 ^ ^ H ψ = E ψ and H ψ = E ψ A A1 1 A1 B B1 1 B1 (a) Suppose that the Hamiltonian of the dimer has the form HA + HB. The first excited state of the dimer will contain one monomer in state 1 and one in state 0. What is the degeneracy of the first excited state? Calculate the energy difference between the ground state and the first excited state of the dimer. (b) Assume that the transition dipole moment of the monomer is written as 2 2 |< ψ | μ | ψ >| = |< ψ | μ | ψ >| = D . A0 A A1 B0 B B1 0 Consider the transition between the ground state and the first excited state of the dimer, calculated the absorption intensity in terms of D0. (c) For the case of two interacting monomers, the Hamiltonian can be written as ^ ^ -3 -5 H + H + V, where V = (μ ‧μ ) R - 3 (μ‧ R ) ( R ‧μ ) R . A B A B AB A AB AB B AB Write down the wavefunctions of the first excited states which are stationary. (d) The so-called exciton splitting refers to the frequency splitting observed for interacting monomers, whereas such splitting is absent for two noninteracting monomers. Explain the origin of exciton splitting. --

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