Triatomic molecules expectation values

In diatomic molecules, T2 = 0, and thus the expectation value of C vanishes. This is the reason why this operator was not considered in Chapter 2. However, for linear triatomic molecules, t2 = / / 0, and the expectation value of C does not vanish. We note, however, that D J is a pseudoscalar operator. Since the Hamiltonian is a scalar, one must take either the absolute value of C [i.e., IC(0(4 2))I or its square IC(0(412))I2. We consider here its square, and add to either the local or the normal Hamiltonians (4.51) or (4.56) a term /412IC(0(412))I2. We thus consider, for the local-mode limit,... 

The ratio CvjCv has been evaluated at 1-29, agreeing fairly well with the figure expected of a substance consisting of triatomic molecules.4 The value falls with rise of temperature as is usual. Thus 5... 

The reaction considered in Example 10.7 involves 3 moles of hydrogen gas on the reactant side and 3 moles of water vapor on the product side. Would you expect AS to be large or small for such a case We have assumed that AS depends on the relative numbers of molecules of gaseous reactants and products. On the basis of that assumption, AS should be near zero for the present reaction. However, AS is large and positive. Why The large value for AS results from the difference in the entropy values for hydrogen gas and water vapor. The reason for this difference can be traced to the difference in molecular structure. Because it is a nonlinear, triatomic molecule, H2O has more rotational and vibrational motions (see Fig. 10.12) than does the diatomic... 

---