Aharon Gedanken

Electronic Energy Transfer Phenomena in Rare Gases

In this paper we present the results of an experimental study of electronic energy transfer in xenon‐argon, krypton‐argon, and xenon‐krypton gaseous mixtures excited by a pulsed electric discharge. Spectroscopic evidence for electronic energy transfer is based on the decrease in the intensity of the vacuum ultraviolet emission of the excited diatomic homonuclear rare gas molecules in the presence of small amounts (10–1000 ppm) of a foreign rare gas atom, while the visible emission spectrum of the host gas is parctically unmodified under these conditions. The relative contributions of two energy transfer mechanisms involving atom‐atom and molecule‐atom energy transfer were established by a kinetic analysis of the dependence of the energy transfer efficiency on the host pressure. We have determined the cross sections for energy transfer from the lowest metastable Ar and Kr excited states, and from the lowest excited state of Ar2* and Kr2* to ground state Xe, and from metastable excited Ar and from Ar2* to g...

Extravalence molecular excitations in inert matrices

In this paper we present the results of an experimental study of extravalence excitations of molecular impurities in solid rare gases and in molecular host matrices. We report the absorption spectra of methyl iodide, benzene, ethylene, and acetylene in solid Ne, Ar, Kr, Xe, N2, and CF4 in the spectral region 2000–1150 A. Spectroscopic evidence has been obtained for the observation of high (n ≥ 2) Wannier impurity states originating from a molecular positive ion. These molecular Wannier series yield spectroscopic information concerning the energetics of molecular photoionization in a dense medium. The large blue spectral shifts of the lowest extravalence molecular excitations in dense media can be rationalized in terms of central cell corrections to the n=1 Wannier state, which are determined by the exciton binding energy.

Emission spectra of solid rare‐gas alloys

In this paper we present the results of an experimental study of the α‐excited vacuum ultraviolet emission spectra of xenon‐argon, xenon‐krypton, krypton‐argon, xenon‐neon, krypton‐neon, and argon‐neon solid alloys in the temperature range 6–40°K. Three mechanisms for electronic energy transfer to single impurity states and to impurity pairs were considered: (1) energy transfer from vibrationally relaxed homonuclear diatomic molecule of the host to Xe/Ar and to Xe/Kr impurity states; (2) energy transfer from the host vibrationally excited homonuclear diatomic molecule to Kr/Ar impurity states; and (3) energy transfer via impurity ionization or the formation of metastable states in neon alloys. The single impurity emission bands originating from the lowest Wannier states exhibit large red Stokes shifts reletive to the corresponding absorption bands, being close to the corresponding gas‐phase transitions, and thus manifest the effect of medium relaxation around single impurity states. A similar effect is ex...

Temperature dependence of the emission spectrum of solid xenon

Abstract We report the temperature dependence of the vacuum ultraviolet emission from the xenon homonuclear molecule in the temperature range 138-23°K. At the highest and lowest temperatures the spectrum consists of a single band peaked at 1720 and 1750A respectively. At intermediate temperatures, 56–83° K, a band peaking at about 1640A dominates the spectrum. This phenomenon is ascribed to temperature induced structural modifications in solid xenon.

Comments on heteronuclear electronically excited rare gas diatomic molecules

Abstract Experimental evidence for the stability of the electronically excited (KrAr) * molecule is presented from the study of the vacuum ultraviolet luminescence spectra of Kr/Ar gaseous, liquid and solid mixtures.

Trapped excitons in solid hydrogen

Abstract A vacuum ultraviolet spectroscopic study of Wannier states of Xe impurity in solid H2 and D2 provides physical information on the conduction band in these solids. We have also observed a large host isotope effect on the optical linewidths of the impurity states.

Emission spectra of homonuclear diatomic rare gas molecules in solid neon

We report the vacuum ultraviolet 1,3Σu→1Σg emission of vibrationally relaxed Ar2*, Kr2*, and Xe2* in solid neon at 6°K. The inhibition of the formation of Ne2* in solid Ne is attributed to the retardation of vibrational relaxation for this diatomic molecule, which is characterized by a relatively high vibrational frequency.

Wannier states of molecular impurity in a liquid rare gas

Abstract We have measured the vacuum ultraviolet absorption spectra of CH 3 I in solid and in liquid krypton in the spectral region 2000–1450 A. In both phases we have observed two Wannier series n ( 2 E 3 2 ) and n ( 2 E 1 2 ) up to n = 3. Information has been obtained concerning the features of the conduction band in a liquid rare gas.

Vacuum ultraviolet spectroscopy of deep lying impurity states in solid CF4

Abstract We have utilized solid carbontetrafluoride as a transparant inert matrix for vacuum ultraviolet spectroscopic studies of impurity states of xenon, methyl iodide and acetylene (in the range 2000-1100 A). n =2 and n =3 Wannier states have been observed leading to quantitative information concerning the conduction band of solid CF 4 . Large blue shifts of the intermediate excited states can be rationalized in terms of central cell corrections to the n =1 Wannier state.

The vacuum UV spectrum of HgBr2

Abstract The band spectrum of HgBr 2 was investigated in the Schuman vacuum uv region (1800 A–1900 A). A new assignment of this spectrum is given. The vibration frequencies for HgBr 2 were found to be: ν 1 ′ = 185 cm −1 ν 1 ″ = 221 cm −1 , ν 2 ′ = 20 cm −1 ν 2 ″ = 53 cm −1 , ν 3 ′ = 224 cm −1 ν 3 ″ = 295 cm −1