Showing papers on "Photoexcitation published in 1975"

Studies of xenon atoms in high Rydberg states

Abstract: Thermal beams of xenon atoms in single high Rydberg states have been produced by photoexcitation of Xe($sup 3$P$sub 0$) metastable atoms. The highly excited states which were populated in this way were identified as np1/2$sub 1$ with 11less than or equal tonless than or equal to16 and nf3/2$sub 1$ with 8less than or equal tonless than or equal to40. The field ionization characteristics and radiative lifetimes of these atoms have been studied.

Photoionization Spectra of Solutions as Obtained by Photoelectron Spectroscopy.

Abstract: : Photoelectron spectroscopic methods with variable photon energy (about 5.2 to 10 eV) are applied to solutions of various photoionizable substances. A recently developed photoelectron spectrometer with continuous renewal of solution is briefly described. Experimental data include: the quantum yield (per incident photon) for photoelectron emission as a function of photon energy; energy distribution curves (EDC) of emitted electrons at given photon energies over the full photon energy range. Photoionization cross sections are obtained by the method of EDC superposition as a function of photon energy. The photoionization spectra thus obtained are discussed, and mechanisms of photoionization are established: direct bound-continuum transitions and autoionization of bound excited states. The following systems are examined: lithium ferrocyanide in glycol, lithium iodide in tetraglyme, ferrocene in tetraglyme, beta-naphthol in glycol. The transfer of kinetic energy from quasifree electrons (generated by optical excitation in the liquid phase) to the liquid medium is briefly treated.

Primary photochemical processes in the vacuum‐uv photolysis of fluoroethylene

Abstract: The vacuum‐ultraviolet (VUV) photolysis of fluoroethylene (FE) has been performed in Ar, N2, Kr, CO, and CO‐doped argon matrices between 8 and 24 K Excitation into various portions of the broad π*←π absorption (λm=1665 A) was effected with N and Br resonance lamps while σ*←σ and/or Rydberg absorptions were excited with the 1216 A H‐resonance line The major elementary processes which occur as a result of photoexcitation are: H2C=CHF+hν → C2H2+HF (1) and H2C=CHF+hν → C2H2F⋅+H (2); where (1) is molecular elimination and (2) a radical producing process Photoexcitation with the Br and H resonance sources also produces fluoroacetylene (FA) via H2C=CHF+hν → C2HF+(HH) (3), to a very small extent Based on relative infrared intensities (1) ? (2) ≫ (3) at all the exciting frequencies The results of concurrent studies involving the difluoroethylenes suggest that (1) and (2) probably occur via internal conversion and intersystem crossing, respectively

The production of photon antibunching by two-photon absorption

Abstract: The two-photon absorption process is, in principle, capable of producing photon beams with second-order coherence less than unity. The dependence of the observability of such values on the initial state of the beam, the absorption path length and the detector sensitivity is outlined. It is concluded that the main problem is not the low intensity involved but rather the low two-photon absorption cross section.

Absence of interference in photoexcitation of triplets

Abstract: Kinetics of growth and decay of triplet states of molecules at known orientation in a magnetic field have been measured. Amplitudes of the zero field eigenstates in each of the eigenstates at finite field were varied by choice of orientation. No interference between the amplitudes of the zero field states was found in the observed kinetics. It is concluded that excitations into the individual zero field components proceed via independent channels.

Conversion of photoexcitation energy in rhodopsin.

Abstract: AN interaction between the 11-cis-retinylidene chromophore and nearest-neighbour molecules seems to be important for explaining the mechanism of conversion of photoexcitation energy, because the chromophore is enveloped by opsin. It has been reported1 that the time of the formation of prelumirhodopsin (lifetime of the excited state) is less than 6 ps.

Formation of supersonic beams of metastable mercury, Hg(6 3P0). Kinetics of photoexcitation and intramultiplet quenching in a nozzle

Abstract: A nitrogen‐seeded supersonic nozzle‐beam source of metastable mercury, Hg(6 3P0),isdescribed.Ground‐state(6 1S0)mercuryisexcited with 2537 A resonance radiation to the 6 3P1 state, which is then converted via intramultiplet quenching to the 6 3P0 state collision with nitrogen (the carrier gas). The mercury beam is accelerated by the N2 seeding gas to a speed of 8×104 cm sec−1. Thus, the present source provides a beam of a single metastable state, Hg(6 3P0), with 4.67 eV of electronic excitation and 0.67 eV of translational energy. The metastable beam has been characterized and the kinetics of the over‐all photoexcitation and quenching process studied by a secondary electron (Auger) detector utilizing a potassium surface, and an electron‐bombardment ionizer, mass‐filter detector. Hg(6 3P0) beam intensities of 4×1012 atoms sr−1⋅sec−1 are obtained, based upon an (assumed) 5% efficiency for the Auger detector.

Emission Spectra of Dimethoxybenzenes by Controlled Electron Impact

Abstract: The emission spectra of o-, m-, and p-dimethoxybenzenes under controlled electron impact excitation (200 eV) were measured in the 220–450 nm region at very low pressures. The photoemissions of the excited parent species and such fragment species as H, CH, CO, and CO+ were observed and assigned. The relative intensities of the photoemissions of the parent species were compared with those of the fluorescence spectra (photoexcitation) in an n-hexane solution. The excited parent species, H, and CH were concluded to be produced in one-electron processes; however, the CO+ species were assumed to be produced in both one- and two-electron processes, and the relative contributions are evaluated. It was concluded that the rate of the predissocation of o-dimethoxybenzene was faster than those of the other two isomers, and the observed characteristics of o-dimethoxybenzene had something to do with this faster rate.

OSO-7 results on coronal emission near 304 A

Abstract: The spectral composition and spatial distribution of equatorial coronal emission near 304 A is examined. Spectral scans indicate that the predominant line is from Si xi. Comparisons of observations with calculations of intensity changes with altitude indicate that collisional excitation is important near the Sun but that photoexcitation becomes dominant beyond about 1.3 R ⊙ from the solar center. Observed and calculated intensities are in approximate agreement for abundances and electron densities that are within the range of observed values.

Film-asymmetry effects in resonant photoexcitation of plasmons

Abstract: The spacings and strengths of plasmon resonances in the optical properties of thin films depend on film symmetry, i.e., on whether the film surfaces are identical or not. Taking account of film asymmetry, the reinterpretation of photoyield data of Anderegg, Feuerbacher, and Fitton explains the fairly systematic alternation of their plasmon-associated resonance strengths and implies that their best-fit values of film thicknesses were about twice too large. (auth)

Studies of Band-Structure, Excitonic Processes and Trap Distribution in Pyrene

Abstract: Photocurrent measurements are used to study conduction-band structure, electron trap characteristics and optical de-trapping processes in pyrene crystals. The spectral yield of the photocurrent arising from photoexcitation of trapped electrons indicates the existance of a series of narrow (0.1 eV) conducting sub-bands which constitute the bottom of the conduction band. A broader band (0.25 eV), about 0.45 eV above the lowest lying conduction sub-band, is also revealed. In the triplet range, de-trapping of electrons by photo-generated triplet excitons is found to be the dominant mechanism. The crystals under study were found to contain three sets of electron traps, each of density of about 5 × 1011 cm−3 located at about 1.35, 2.07 and 2.4 eV below the lowest conduction band. The cross sections for direct photoexcitation and for de-trapping of electrons by triplet excitons are 5 × 10−17 cm2 and ∼ 10−15 cm2 respectively for the first set, and 5 × 10−18 cm2 and ∼ 10−16 cm2 for the second set of traps.

Emission spectra of dimethoxybenzenes by controlled electron impact

Abstract: The emission spectra of o-, m-, and p-dimethoxybenzenes under controlled electron impact excitation (200 eV) were measured in the 220–450 nm region at very low pressures. The photoemissions of the excited parent species and such fragment species as H, CH, CO, and CO+ were observed and assigned. The relative intensities of the photoemissions of the parent species were compared with those of the fluorescence spectra (photoexcitation) in an n-hexane solution. The excited parent species, H, and CH were concluded to be produced in one-electron processes; however, the CO+ species were assumed to be produced in both one- and two-electron processes, and the relative contributions are evaluated. It was concluded that the rate of the predissocation of o-dimethoxybenzene was faster than those of the other two isomers, and the observed characteristics of o-dimethoxybenzene had something to do with this faster rate.

Primary photochemical processes in the vacuum-uv photolysis of fluoroethylene

Abstract: The vacuum‐ultraviolet (VUV) photolysis of fluoroethylene (FE) has been performed in Ar, N2, Kr, CO, and CO‐doped argon matrices between 8 and 24 K. Excitation into various portions of the broad π*←π absorption (λm=1665 A) was effected with N and Br resonance lamps while σ*←σ and/or Rydberg absorptions were excited with the 1216 A H‐resonance line. The major elementary processes which occur as a result of photoexcitation are: H2C=CHF+hν → C2H2+HF (1) and H2C=CHF+hν → C2H2F⋅+H (2); where (1) is molecular elimination and (2) a radical producing process. Photoexcitation with the Br and H resonance sources also produces fluoroacetylene (FA) via H2C=CHF+hν → C2HF+(HH) (3), to a very small extent. Based on relative infrared intensities (1) ? (2) ≫ (3) at all the exciting frequencies. The results of concurrent studies involving the difluoroethylenes suggest that (1) and (2) probably occur via internal conversion and intersystem crossing, respectively.