Doublet–quartet conversion in negative ions as a possible mechanism of the electron autodetachment delay

Abstract

Molecular negative ions with abnormally high lifetimes (20 micros) relative to electron autodetachment were registered at 1.65 eV electron energy in pyromellitic acid imide by means of negative ion mass spectrometry with resonant electron capture. Using quantum-chemical calculations, it was shown that the delay of the electron autodetachment may be caused by the conversion of an originally generated molecular ion-doublet into a molecular ion-quartet, as a result of intersystem crossing of the potential energy surfaces of these ions. It was noticed that the ion-quartet cannot decay rapidly into the molecule of the ground state because of the prohibition of the spin flip, which is similar to that for phosphorescence. It can also not decay into the parent triplets, because these triplets are higher in energy than the ion. As a whole, both prohibitions provide the observed effect of the high lifetime of the ions.

DFT theoretical studies of anions of aniline and its several derivatives

“…[6]. This correlation was explained within the quantum mechanical approach [7,8] where the long lifetime of negative ions was related to the appearance of doublet-quartet state crossing in negative molecular ions which is similar to phosphorescence in neutral molecules.…”

Anomalously long‐lived molecular negative ions of duroquinone

“…For the case of polyatomic organic molecules, this idea was put forward first by Allan . This was done in a brief form (see page 317 of Allan), and then it was offered independently by us . In the quartet conception, Q M – is reported as a long‐lived ion, since all decay channels of the electron autodetachment from it are either delayed or fully closed.…”

“…As a result, the anomalously long‐lived M – ions appear. Previously, we used this concept to explain the anomalously long‐lived M – ions of pyromellitic acid imide, para ‐benzoquinone and duroquinone, and then for consideration of the NDR effect in duroquinone…”

“…Additionally, processes on surfaces under an electrical voltage (which also often involve the REC mechanisms) are currently studied with various experimental approaches from microelectronic devices to scanning tunneling microscopy (STM) . Some time ago we reported results from gas‐phase REC principles, which may be directly used to understand some condensed matter processes, in particular the processes occurring in nanoelectronic devices with a single molecule placed between two electrodes. As a result our first attempt to advance this was performed with duroquinone (2,3,5,6‐tetramethyl‐1,4‐benzoquinone) .…”

Разброс В Измерениях Времени Жизни Отрицательных Ионов Как Следствие Их Адсорбции На Стенках Камеры Ионизации

“…Как результат, колебательная энергия иона уменьшается, и он оказывается ниже того коле-бательного уровня, на котором образовался. С другой стороны, по нашим данным, ион DQ − образуется в квартетном состоянии посредством интеркомбинацион-ной конверсии из материнского иона-дублета за счет безызлучательного перехода с инверсией электронного спина в точке пересечения поверхностей потенциаль-ной энергии " исходного" (материнского) иона-дублета и иона-квартета [15][16][17][18]. Переход иона-квартета на более низкий колебательный уровень уводит его " вниз" по энергии от точки пересечения с материнским дублетом, препятствуя тем самым его возвращению в дублет, откуда он быстро распался бы.…”