Europhys. Lett.
Volume 68, Number 3, November 2004
Page(s) 377 - 383
Section Atomic and molecular physics
Published online 09 October 2004
Europhys. Lett., 68 (3), pp. 377-383 (2004)
DOI: 10.1209/epl/i2004-10225-3

Low-energy positron scattering: Modelling the formation of bound $\mth{[M\mbox{-}e^+]}$ states in deformed polyatomic molecules

T. Nishimura and F. A. Gianturco

Dipartimento di Chimica, Università di Roma "La Sapienza" and INFM Piazzale A. Moro 5, 00185 Roma, Italy

received 12 May 2004; accepted in final form 10 September 2004
published online 9 October 2004

Quantum calculations are carried out to evaluate the scattering length A0 for low-energy positron collisions with gaseous acetylene molecules which are being "distorted" in their $\nu_5$ vibrational mode during the scattering. As the molecular structure undergoes increasingly larger distortions of that bending mode, the clear signature of a metastable state (change of sign for A0) appears at bending deformation of about $16^{\circ}$ from the linear geometry. The effects of such state on the size of the annihilation parameters of the title molecule are evaluated and the implications for larger polyatomics are discussed.

34.85.+x - Positron scattering.
36.10.Dr - Positronium, muonium, muonic atoms and molecules.
34.50.Ez - Rotational and vibrational energy transfer.

© EDP Sciences 2004