Negative ion adsorption by the ion source surface as a factor influencing ion lifetime measurements

Abstract

ÓÂÔÔÏÑÕÓÇÐËâ ËÊÖÚÇÐÞ ÓÂÊÎËÚÐÞÇ ÂÔÒÇÍÕÞ ÒÓÑÙÇÔÔ ²©¿, ÕÂÍËÇ ÍÂÍ ÄÊÂËÏÑAEÇÌÔÕÄËÇ AEËÔÍÓÇÕÐÑÅÑ Ë ÔÒÎÑÛÐÑÅÑ ÔÒÇÍÕÓÑÄ Ô ÄÞØÑAEÑÏ Ð ÄÇÎËÚËÐÖ ÄÓÇÏÇÐË ÉËÊÐË t a ËÑРa M À ÑÕÐÑÔËÕÇÎßÐÑ ÂÄÕÑÑÕÜÇÒÎÇÐËâ AEÑÃÂÄÑÚÐÑÅÑ àÎÇÍÕ-ÓÑР[11]. ³×ÑÓÏÖÎËÓÑÄÂÐÑ ÒÑÐâÕËÇ "×ÂÍÕÑÓ ÄÞÉËÄÂ-ÐËâ", ÑÒÓÇAEÇÎâáÜÇÅÑ ÔÑÑÕÐÑÛÇÐËÇ ÍÑÐÍÖÓËÓÖáÜËØ ÍÂ-ÐÂÎÑÄ ÓÂÔÒÂAE ì ÂÄÕÑÑÕÜÇÒÎÇÐËâ Ë AEËÔÔÑÙËÂÙËË, ÒÑÎÖ-ÚÇÐÑ ÕÇÑÓÇÕËÚÇÔÍÑÇ ÄÞÓÂÉÇÐËÇ AEÎâ ÔÇÚÇÐËâ s ÊÂØÄÂÕ àÎÇÍÕÓÑРÏÑÎÇÍÖÎÑÌ [18]. ªÊÏÇÓÇÐÐÞÇ ÊÐÂÚÇÐËâ t a ÔÑ-ÔÕÂÄËÎË ÑÔÐÑÄÖ ÏÑAEÇÎÇÌ, ÖÚËÕÞÄÂáÜËØ ÓÑÎß ÄÑÎÐÑÄÑÌ ×ÖÐÍÙËË âAEÇÓÐÑÌ ÒÑAEÔËÔÕÇÏÞ ÔËÔÕÇÏÞ ÏÑÎÇÍÖΠë àÎÇÍÕ-ÓÑÐ, ËÊÏÇÐÇÐËâ ÍÑÐ×ËÅÖÓÂÙËË âAEÇÓ Ä ÒÓÑÙÇÔÔÇ àÄÑÎáÙËË ÑÕÓËÙÂÕÇÎßÐÑÅÑ ËÑРÒÑÔÎÇ ÇÅÑ ÑÃÓÂÊÑÄÂÐËâ, ÔÑÑÕÐÑÛÇ-ÐËâ àÎÇÍÕÓÑÐÐÞØ ÕÇÓÏÑÄ ËÑÐÂ Ë ÏÂÕÇÓËÐÔÍÑÌ ÏÑÎÇÍÖÎÞ [4,7,8] It is well known that negative ions that form in the gas phase due to low-energy electron capture by molecules show a scatter in the measured lifetimes of their autodetachment states. In considering this problem, it is found that when using a static sector magnetic mass spectrometer, some of the ions that form on the ionization chamber walls are adsorbed and stabilized there and then join the registered ion êow, thereby distorting the measured lifetime. Because the number of the adsorbed ions depends on the experimental conditions, their contribution to the total êow is to some extent uncontrollable ì hence the scatter.