The potential energy function for the force between two atoms in a diatomic molecule is approximately given by $U ( x ) = \frac { a } { x ^ { 12 } } - \frac { b } { x ^ { 6 } }$, where a and $b$ are constants and $x$ is the distance between the atoms. If the dissociation energy of the molecule is $D = \left[ U ( x = \infty ) - U _ { \text {at equilibrium} } \right]$, $D$ is (1) $\frac { b ^ { 2 } } { 2 a }$ (2) $\frac { b ^ { 2 } } { 12 a }$ (3) $\frac { b ^ { 2 } } { 4 a }$ (4) $\frac { b ^ { 2 } } { 6 a }$
The potential energy function for the force between two atoms in a diatomic molecule is approximately given by $U ( x ) = \frac { a } { x ^ { 12 } } - \frac { b } { x ^ { 6 } }$, where a and $b$ are constants and $x$ is the distance between the atoms. If the dissociation energy of the molecule is $D = \left[ U ( x = \infty ) - U _ { \text {at equilibrium} } \right]$, $D$ is\\
(1) $\frac { b ^ { 2 } } { 2 a }$\\
(2) $\frac { b ^ { 2 } } { 12 a }$\\
(3) $\frac { b ^ { 2 } } { 4 a }$\\
(4) $\frac { b ^ { 2 } } { 6 a }$