How to assign initial and final states of iodine transitions in its spectrum?

In an experiment, I gently heated iodine crystals to create vapors and then observed it absorption spectrum with a spectrometer. The temperatures throughout were moderate (maximum $40^\circ\text{C}$). I observed a series of dark bands from red region to blue-green region with spacing between consecutive bands decreasing from red end towards to blue end.


I calculated the wavelengths corresponding to these bands beginning from the first resolvable band in the red region and ending at the $30^{th}$ reading (without missing a single dark band *in between*). The data is as follows:


$$\begin{array}{c|c} 
 \text{Colour Region} & \lambda/\text{nm} \\ \hline
\text{Red} & 624.884 \\
& 624.884 \\
& 621.831 \\
& 617.552 \\
\text{Orange} & 612.581 \\
& 609.518 \\
& 606.070 \\
& 601.798 \\
& 597.629 \\
& 594.171 \\
& 591.095 \\
\text{Yellow} & 586.862 \\
& 584.243 \\
& 581.853 \\
& 577.225 \\
\text{Yellow-Green} & 575.218 \\
& 571.819 \\
& 567.954 \\
& 565.246 \\
\text{Green} & 562.924 \\
& 560.291 \\
& 557.579 \\
& 554.399 \\
& 551.684 \\
& 550.053 \\
& 548.422 \\
& 547.490 \\
& 544.693 \\
& 541.271 \\
& 540.027 \\
& 538.548 \\
\text{Blue-Green}
\end{array}$$


Now, in order to obtain information about the parameters like bond dissociation energy, convergence limit, etc., I need to know the quantum numbers which correspond to each observed transition wavelength which are the initial and final electronic states and the vibrational states.


**Question:** How to find these? I know that generally, sources characterize some 
*standard* states, like [this](http://homepages.gac.edu/~anienow/CHE-372/Labs/I2lab.pdf) says that $541.2\text{ nm}$ corresponds to $v''=0\rightarrow v'=27$. But what am I supposed to do with the larger wavelengths? Cuz the sources say that Franck-Condon prohibits $v''=0$ to low $v'$ transitions. But nevertheless, I do am observing larger wavelengths. Are these from $v''>0$?  

How can I even be sure that these are $X\rightarrow B$ transitions? Cuz of operating temperatures?


Please provide some proper approach!




---


The difficulties that I am facing in this assignment of states are also elucidated in [this](https://chemistry.stackexchange.com/questions/127328/observing-bands-which-i-shouldnt-be?noredirect=1#comment244737_127328) post of mine.


