The extinction coefficient is equal to the absorbance divided by the thinkness of the sample.

If you mean the molar extinction coefficient \eps\ then it is givent by A=\eps\lC where A is the absorbance, l the thinkness of the sample, C the concentration. Take care to the units. Chemists are using strange ones.

You cannot measure the refraction index from you data. Except if you record the absorbance over all the absorption spectrum and utilse the  Kramers–Kronig relation. This is not realy working.

If by chance, you can see oscillations of the baseline in the transprent spectral region of your sample and if your sample is a thin layer then you can calculate the refraction index according to :

Swanepoel, R. "Determination of the Thickness and Optical-Constants of Amorphous- Silicon." J Phys E Sci Instrum, 1983, 16, 1214-1222.

Thank you Mr.Robert Bernard Pansu for your suggestion. During the calculation of Extinction coefficient what is the unit of thickness? My sample thickness is 100 nm. I want to know what is the unit of thickness during calculation. 

Please refer to the attached paper ....

you can use the PUMA software for the determination of the constants optic from transmission data. but you must have a knowledge about the thickness intervalle. 

http://www.ime.usp.br/~egbirgin/puma/

Prof. Nabeel, I am interested in using the method in the recommended paper as a complementary method to obtain the n and k of some films. Could you please clarify further how to obtain Tm, ne1 and ne2 in eqns 1 and 3 respectively. Are they based on the deconvoluted peaks?

Also, how is ln(x) different from ln(1/T) which is usually used to obtain alpha?