There seems to be two schools of thought about the raga of this song. Some call it Gamakakriya, which may or may not be another raga, as it shares the same scale. One thought is that it is just the old name for Purvikalyani. I do not have the knowledge to discuss this; I will just call it Purvikalyani as I had thought of it for many years. For knowledgeable readers, there is an excellent article on Purvikalyani here.
The scales of Purvikalyani are as follows :
Aarohanam (Ascending) : S R1 G3 M2 P D2 P S’
Avarohanam (Descending) : S’ N3 D2 P M2 G3 R1 S
Purvikalyani is a janya raga, derived from Gamanashrama (below), 53rd on the Melakarta scale.
Well known compositions in Purvikalyani are Meenakshi Me Mudam by Muthuswami Dikshithar, Karanam Kettu Vadi by Gopalakrishna Bharathi, O Rama Nee Nama by Bhadrachala Ramadas and Parama Pavana Rama by Poochi Srinivasa Iyengar.
Note : The 12 notes in the octave are named as below. Please note that C is used as Sa for the sake of simplicity as the scale is relative in Carnatic Music. Also note that the scales paint only a superficial picture of the raga as the gamakas(ornamentations) are a very important part of a raga.