Momentum of intertia for a dihydrogen molecule

[fab13]

Homework Statement

The rotational energy level of a symmetric molecule like H2 are given by :

$En = n(n + 1)h^{2}/(2J)$

where $J$ is the momentum of inertia of the molecule. Compute the energy of the first rotational level in eV.

the following information is given : distance between the proton in H2: $74.14 pm$

Relevant Equations

I have used the following equation for momentum of inertia : $J=MR^{2}$ with $M$ the total mass and $R$ the radius of rotation.

I don't know if the value for distance between protons given in the homework is right ($d = 74.14 pm$).

Indeed, on the following link : https://brainly.in/question/7147660 , they take a distance equal to $d = 4\times10^{-10} m$.

In all cases, the same formula is applied : $J=2\,m_{p}\,(\dfrac{d}{2})^{2} = m_{p}\,d^{2}/2$

Which value for distance between the 2 protons have I to take ? $74.14$ pm or $4\times10^{-10} m$ ?

Thanks for your help.

 

[haruspex]

http://hitoshi.berkeley.edu/221B-S02/molecular.pdf agrees with the 74.14 10^-12m figure.

 

[fab13]

thanks !