Collisional excitation of vinylidene (H2CC).

Though H 2 CO, H 2 CS, H 2 CCC, H 2 CCCC, H 2 CCO have been identified in cool interstellar molecular clouds, identification of H 2 CC is still awaited. To analyze its spectrum, collisional rate coefficients are required. We have calculated collisional rate coefficients for rotational transitions between 23 levels of ortho and para H 2 CC for kinetic temperatures 10, 20, 30, 40, and 50 K. The scattering problem is analyzed using the computer code MOLSCAT where the colliding partner is He atom. The interaction between H 2 CC and He has been calculated with GAUSSIAN 2003. For the interaction potential obtained with GAUSSIAN 2003, MOLSCAT is used to derive the parameters q ( L , M , M ′ | E ) as a function of energy E of the colliding partner. After averaging the parameters q ( L , M , M ′ | E ) over a Maxwellian distribution, the parameters Q ( L , M , M ′ | T ) as a function of the kinetic temperature T in the cloud are obtained. Finally, the collisional rate coefficients have been calculated. We have also calculated radiative transition probabilities for the transitions between the rotational levels. Finally, for ortho-H 2 CC, we have solved a set of statistical equilibrium equations coupled with the equations of radiative transfer and found that the H 2 CC may be identified through anomalous absorption of its transition 1 11 – 1 10 at 4.89 GHz. [ABSTRACT FROM AUTHOR]