Importance of the multicenter character of molecular aggregates in the theoretical description of the charge transfer process S.E. Corchs * , H.F. Busnengo, R.D. Rivarola Instituto de F  õsica Rosario, CONICET-UNR and Facultad de Ciencias Exactas, Ingenier  õa y Agrimensura, UNR, Av. Pellegrini 250, 2000 Rosario, Argentina Received 25 August 1998; received in revised form 3 November 1998 Abstract In the present work we focus our interest on the electron capture process from H  2 by proton impact at high impact energies. The molecular-continuum distorted wave (M-CDW) and the corresponding two eective center (TEC-CDW) approximations are used to compute single dierential (as a function of the molecular alignment) and total electron capture cross sections. In the M-CDW approximation the ®eld created by both nuclei of the target is considered to act simultaneously on the electron in the exit channel. On the contrary, in the TEC-CDW approximation each one of these nuclei is considered to aect separately the captured electron. Then, the importance of the eects due to this multicenter character of molecular aggregates in the charge transfer process is studied through the comparison of theoretical cross sections obtained with both approximations for the H   H  2 system. It is found that multicenter eects are important for the study of dierential cross sections as a function of the molecular orientation but they do not modify signi®cantly the total cross sections. The origin of this behavior is interpreted in terms of the impact parameter dependence of the capture probability. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 34.70.+e 1. Introduction The theoretical description of electron capture processes from molecular targets presents more diculties compared with the atomic target case due to the multicenter character of the molecules. From a theoretical point of view, H  2 is the sim- plest molecular target to study. However, H 2 is the simplest molecular target for which there exist experimental data of single capture. In order to compare with these data, several works have been devoted to the theoretical description of such re- actions (see [1±13] and references therein). In particular, the two eective center approximation (TEC) has been widely used with success in the calculation of total cross sections. Within the dis- torted wave formalism, and using the one active electron model the TEC approximation has been introduced in a simple way [13]. In the entrance channel, the active electron is shared by both Nuclear Instruments and Methods in Physics Research B 149 (1999) 247±256 * Corresponding author. Tel.: +54 41 495467; fax: +54 41 802654; e-mail: scorchs@fceia.unr.edu.ar 0168-583X/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 8 ) 0 0 9 3 4 - 3