Collisional rates for vib-rotational transitions in diatomic molecules^*

¹ School of Physical Sciences, Swami Ramanand Teerth Marathwada University, Nanded 431 606, India
² B.R.C.M. College of Engineering and Technology, Bahal 127 028, India

Corresponding author: S. Chandra, chandrasuresh@123india.com

Received: 19 May 1999
Accepted: 28 May 2001

Abstract

A number of diatomic molecules have been found in vibrationally excited states in several cosmic objects. The molecules in vibrationally excited states provide valuable information about the physical conditions prevailing near star forming regions and in circumstellar envelopes of late-type stars. To analyze the spectrum of such molecules, some of the important parameters required are the collisional rate coefficients for vib-rotational transitions in the molecule. Currently, knowledge of collisional rate coefficients is very poor. Here, we discuss a method for calculating the collisional rate coefficients for vib-rotational transitions in a diatomic molecule, where the colliding partner H₂ is considered as a structureless particle. This method is quite good for high temperatures (usually found in star-forming regions and in circumstellar envelopes of late-type stars), but may be questioned for low temperatures. As an example, calculations for the CS molecule at 500 K for three vibrational states are presented.