(molecular spectroscopy)what is the meaning of the symbol

[einstein1921]

Hi, everyone. In the picture attached, what is the meaning of 0oo? what should I read to understand the meaning?Thank you!

 

[DrDu]

I suppose it is some symbol for vibrational modes excited. Maybe you could write something about what is measured? Is this a mass spectrum after two photon excitation?

 

[einstein1921]

I suppose it is some symbol for vibrational modes excited. Maybe you could write something about what is measured? Is this a mass spectrum after two photon excitation?

thank your for your answer! I also think it should be vibraitonal modes exceted. However, what confused me is that 0 to 0 transition is non-meaningful! attached is the paper!

 

[DrDu]

From the paper and ref. 6 therein I understand that the big number is the $\nu_1$ number of the excited state while the small superscript is the $\nu_2$ quantum number of the excited state.
The sub-script is the $\nu_2$ vibrational number of the ground state.
I suppose that due to the higher frequency, the $\nu_1$ mode is never excited in the ground state.
$\nu_1$ is the symmetric stretch and $\nu_2$ the out of plane bending mode.

Why is a 0 to 0 transition not meaningful? Take in mind that in electronic transitions, in contrast to IR or Raman purely vibrational transitions, vibrational levels don't have to change (with the exception of symmetry forbidden transitions). See e.g.:
http://en.wikipedia.org/wiki/Franck–Condon_principle