We can apply the rigid rotor approximation to the rotational energy levels of a diatomic molecule, with E, = BJJ + 1), where B represents a rotational constant. (a) Given the selection rules for ro-vibrational transitions, develop a formula for an absorption in the R branch from a state with angular momentum J. Assume a harmonic oscillator vibration with frequency 785 cm¹ originating in the ground vibrational state (i.e. n = 0). You will be given a value for B and asked to compute the energy for a particular transition on the submission quiz. -1 (b) Suppose you measure several R-branch rotational transitions for 24Mg¹60, and you find that the absorption lines are uniformly spaced 1.1485 cm-¹ apart. The quantity, B, represents a rotational constant related to the moment of inertia, /, of the molecule, via h

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We can apply the rigid rotor approximation to the rotational energy levels of a diatomic
molecule, with E, = BJ(J + 1), where B represents a rotational constant.
(a) Given the selection rules for ro-vibrational transitions, develop a formula for an
absorption in the R branch from a state with angular momentum J. Assume a harmonic
oscillator vibration with frequency 785 cm¹ originating in the ground vibrational state
(i.e. n = 0). You will be given a value for B and asked to compute the energy for a
particular transition on the submission quiz.
(b) Suppose you measure several R-branch rotational transitions for 24Mg¹60, and you find
that the absorption lines are uniformly spaced 1.1485 cm-¹ apart. The quantity, B,
represents a rotational constant related to the moment of inertia, I, of the molecule, via
h
B =
8π² cl
when expressed in wavenumber (cm-¹) units. Based on this information, what is the
value of the moment of inertia (in kg-m²) for MgO?
(c) Using the results you have found, what is the bond length for MgO in pm?
Transcribed Image Text:We can apply the rigid rotor approximation to the rotational energy levels of a diatomic molecule, with E, = BJ(J + 1), where B represents a rotational constant. (a) Given the selection rules for ro-vibrational transitions, develop a formula for an absorption in the R branch from a state with angular momentum J. Assume a harmonic oscillator vibration with frequency 785 cm¹ originating in the ground vibrational state (i.e. n = 0). You will be given a value for B and asked to compute the energy for a particular transition on the submission quiz. (b) Suppose you measure several R-branch rotational transitions for 24Mg¹60, and you find that the absorption lines are uniformly spaced 1.1485 cm-¹ apart. The quantity, B, represents a rotational constant related to the moment of inertia, I, of the molecule, via h B = 8π² cl when expressed in wavenumber (cm-¹) units. Based on this information, what is the value of the moment of inertia (in kg-m²) for MgO? (c) Using the results you have found, what is the bond length for MgO in pm?
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