Absorption Spectra of Metals in Solution

Abstract

Measureme~lts of the absorption spectra were made on solutions of allcali and allcaline earth metals in ammonia, methylamine, ethylarnine, and ~nixecl solvents. I n ammonia, a single absorption band was measured which is common to all the ~netals esamined. I n the arnines and in mixtures of arnlno~~ia mith methylamine, ho~vever, bands were found which were characteristic of the metal employed. h hypothesis has been advanced to explain the existence of the different types of energy traps responsible for the variations in spectra.The alliali metals ancl some of the a l l d i n e earth metals dissolve in liquid ammonia without reaction; it is thought that simple dissolution occurs, yielding metal ions and electrons xxrl~ich are trapped or solvated in the liquid (5). Various physical properties have been examined whiclz are consistent mith this postulate, although a concise model has not yet been formulated for the electron traps. For example, the expansion exhibited on dissolving the metal has been attributed t o the formation of holes in the liquid which represent energy barriers for the escape of electrons (8). The electrical conductivity in dilute solution is greater than can be explained by simple ionic transport, but less than mould be expected by electronic conduction (5). Magnetic susceptibility measurements indicate that the metal is ionized, but some difficulty is experienced in explaining the variation of the susceptibility with temperature (3). The measurements of paramagnetic resonance absorption are consistent with the existence of trapped electrons (4). Finally, the absorption spectra of a number of the solutions have been measured, and the observation made that in ammonia there is a single absorption maximum whose position is independent of the particular metal in solution (1, 9). This maximum is in a region where none appears in the spectrum of bullr sodium metal; ancl in the spectrum of atomic sodium, very strong absorption occurs a t 5889 i % (D line), which does not appear in the solution spectrum. Since the maximum observed is also absent from the spectrum of sodium ion and of liquid ammonia, it has been ascribed t o the trapped electrons.Primary amines will also dissolve some of the metals; sodium, cesium, potassium, lithium, and calcium are soluble in methylamine, ~vhile ethylarnine dissolves a t least lithium and potassium. Although these solutions have been exaininecl lcss exhaustivelj. than the ammonia solutions, their behavior is similar. Thus the variation of electrical conductivity with concentration in metal solutions in methylamine is similar t o that in anhydrous alnmonia (2), and the absorption spectra, although exhibiting maxima a t a different wave l11hnzrscript

Correlation of optical and electron spin resonance spectra for alkali metal solutions in ethylamine and tetrahydrofuran

“…Optical absorption spectra in these same solutions are, in general, composed of two bands attributed to metal-dependent and metal-independent species. The former or 'visible' band occurs in the region 10 000 -15 000 cm-I and has been assigned to the diamagnetic species M-(11-16), whereas the latter band, which extends further into the infrared (<7000 cm-'1, has generally been identified with solvated electrons, e,-, (11, 14,15,[17][18][19][20]. Ion-pair species, (M+, e,-) (14, 151, have also been suggested as contributing to the infrared absorption.…”

Pulse Radiolysis of Alkali Metal Solutions in Ethylamine

“…2, 3, 9, and 10). We suggest therefore that in ethylamine the true e,-absorption has a maximum at >, 1800 nm, a wavelength significantly different from the infrared band maxima of 1400-1600 nm normally attributed to e,-in alkali metal solutions (19)(20)(21). The rate of formation of the 1400 n m band is metal dependent (Table 1) and for 2.5 x lop4 M sodium and 4.5 x lop4 M potassium solutions the species is present in significant concentration 5 ps after the pulse (Fig.…”

“…Hitherto it has been common to assign the longer wavelength infrared absorptions to the solvated electron (19)(20)(21). This is supported in , ,…”

Bildungsreaktionen und Eigenschaften solvatisierter Elektronen

“…In Verbindung mit den Molvolumina der üb-rigen an der Reaktion beteiligten Stoffe ergibt sich der [31,34,[65][66][67][68] (bei der Elektronenbestrahlung) und für Ammoniak [69][70][71][72][73] - [77] treten nicht etwa die zwei für die beiden Lösungsmittel charakteristischen Absorptionsmaxima auf, sondern nur ein einziges dazwischen liegendes Absorptionsmaximum, dessen Lage von der Lösungsmittelzusammensetzung abhängt [31,70,71,77]. Deuterierung [35, 7S, 79] und Elektrolytzusatz [73,SO] verschieben das Absorptionsmaximum nach etwas höheren (8) höheren Für wäßrige Lösungen wird das Normalpotential dergelö-sten Elektronen aus der Summe der freien Reaktionsenthalpien der Reaktionsfolge ergibt die Abschätzung eine so kleine Gleichgewichtskonstante, daß ein Nachweis der gebildeten Elektronen bei Zimmertemperatur aussichtslos erscheint.…”