c) Find the value of r for which U is a minimum. d) What is the minimum value of U?

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Chapter1: Units, Trigonometry. And Vectors
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Please give the answers of c d step by step 

**Vibrational Excitations in Diatomic Molecules**

Vibrational excitations in a diatomic molecule can be described with a potential energy function of the form:

\[ U(r) = D(e^{-2a(r - r_e)} - 2e^{-a(r - r_e)}) \]

where \( r \) is the interatomic distance, \( r_e \) is the equilibrium bond distance, \( D \) is the dissociation energy (a constant), and \( a \) is a positive constant.

### Questions

**a)** What are the dimensions of \( r_e, D, \) and \( a \)? Express your answer in terms of products \( L^a T^b M^c \), where \( L \) is length, \( T \) is time, \( M \) is mass, and \( a, b, \) and \( c \) are rational numbers.

**b)** What is the value of the potential at arbitrarily large separations (\( r \gg r_e \))?

**c)** Find the value of \( r \) for which \( U \) is a minimum.

**d)** What is the minimum value of \( U \)?

**e)** Show that for very small displacements \( x = (r - r_e) \ll 1 \), the potential energy can be approximated to

\[ U(x) - U(0) = \frac{1}{2}kx^2 \]

where \( k = 2a^2D \).
Transcribed Image Text:**Vibrational Excitations in Diatomic Molecules** Vibrational excitations in a diatomic molecule can be described with a potential energy function of the form: \[ U(r) = D(e^{-2a(r - r_e)} - 2e^{-a(r - r_e)}) \] where \( r \) is the interatomic distance, \( r_e \) is the equilibrium bond distance, \( D \) is the dissociation energy (a constant), and \( a \) is a positive constant. ### Questions **a)** What are the dimensions of \( r_e, D, \) and \( a \)? Express your answer in terms of products \( L^a T^b M^c \), where \( L \) is length, \( T \) is time, \( M \) is mass, and \( a, b, \) and \( c \) are rational numbers. **b)** What is the value of the potential at arbitrarily large separations (\( r \gg r_e \))? **c)** Find the value of \( r \) for which \( U \) is a minimum. **d)** What is the minimum value of \( U \)? **e)** Show that for very small displacements \( x = (r - r_e) \ll 1 \), the potential energy can be approximated to \[ U(x) - U(0) = \frac{1}{2}kx^2 \] where \( k = 2a^2D \).
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