Photon Absorption Process Research Articles

Inelastic scattering of light and transitions of colliding atoms to bound molecular states

A study is made of the influence of photon absorption (emission) processes on the dynamics of collisions between two atoms. Under certain conditions the radiation field can transfer colliding atoms to a bound molecular state. The main contribution to these processes is made by atoms colliding with relative velocities and impact parameters which ensure that these atoms spend a long time near each other (quasifinite motion). The appearance of quasifinite states in the absorption spectra of Rb and Cs vapors is reported and a determination is described of the matrix elements of the transitions from these states to a bound molecular state.

Observation of the Faraday effect with 230 keV and 330 keV photons

The F a r a d a y effect is a useful tool for inves t iga t ing the spin dependence of photon absorpt ion processes (see, for instance, rcf. (~)). I t arises from a polar izat ion dependence of the re f rac t ive index n of a magnct izcd optical medium. When l inearly polarized l ight passcs th rough a magnet ized ~bsorbcr, the polar izat ion vect(,r ro ta tes around the beam direct ion by an angle of

CO(a 3Π), Its Production, Detection, Deactivation, and Radiative Lifetime

This paper describes the first reported observation of the CO Cameron bands (a 3Π→X 1Σ+) produced from CO through photon absorption processes. The technique depends on quasiresonance fluorescence processes involving d 3Δ↔X 1Σ+ and a′ 3Σ+↔X 1Σ+ transitions and subsequent radiation from these triplet levels to the a 3Π state. From experiments in which the exciting lamp is pulsed, time decay measurements permit evaluation of the quenching rate constants for CO(a 3Π) by CO, NO, O2, H2, and CO2. The radiative lifetime of CO(a 3Π) has been obtained by use of the quenching rate constants, the intensities of the a 3Π populating transitions, and the Cameron band intensities, and it has an average value of 4.4±1.1 msec. Transfer of electronic energy takes place from CO(a 3Π) to NO, resulting in production of two radiating states, NO(A 2Σ) and NO (B 2Π), with approximate efficiencies of 23% and 10%, respectively. Either of these may be used as a monitor of the CO(a 3Π) state. Quenching of CO(a 3Π) by N2 leads to production of N2(A 3Σu+), but rate constants will have to be evaluated as a function of the degree of CO(a 3Π) vibrational excitation.

Electron Spin Resonance Study on Ultraviolet Light Irradiated Benzene Adsorbed on Silica Gel and Alumina

Abstract Benzene adsorbed on silica gel was irradiated at 77°K with ultraviolet light. Three kinds of samples, with different degree of adsorption, were examined. ESR spectra were strongly dependent on the amount of benzene adsorbed and three different spectra were observed; (1) six-line spectrum with a splitting value of 6 gauss, assigned to phenyl radical, (2) seven-line spectrum with a splitting value of 4.5 gauss, assigned to benzene cation radical, and (3) apparent nine-line spectrum with 2.4 gauss splitting due to benzene dimer cation radical. Upon raising temperature, benzene cation radical was found to transform into benzene dimer cation radical. In UV-irradiated benzene-alumina system, cyclohexadienyl radicals were observed in addition to the ion radicals. It is suggested that the above reaction may be occurred by two photon absorption process involving the excitation of triplet benzene.

Study of Electroabsorption Using Differential Photocurrent Response

A method is devised to study the tunneling-assisted photon absorption process (Franz-Keldysh effect) in semiconductor junctions, making use of the differential photocurrent response. This method has advantages over the differential-transmission method in the region of high absorption coefficient. Measurements were made using this technique on GaAs, Ge, and Si $p\ensuremath{-}n$ junctions. The results on GaAs and on Ge are in qualitative agreement with theory and with published results of transmission measurements. No theory is available corresponding to the results of silicon.

Recent Instrumentation for the Optical Studies of Solids in the Vacuum Ultra-Violet

Recent progress in vacuum ultra-violet instrumentation and techniques useful to solid state physics is described, although much of the instrumentation advances are also of use to other V-uv studies. Improvements in sources, detectors, and dispersive systems (particularly in grating reflectivities) are noted. While commercial instrumentation is not described, it is perhaps in this area that the most striking instrumental progress has come. Besides optical studies, work on internal and external photoemission continues to augment the optical work. Interest in luminescent systems is also still useful as indicating something about the energy band scheme in insulating solids. An important advance is noted wherein use is made of laser radiation in conjunction with ultra-violet radiation in a double photon absorption process in KI.

Energy Distributions of Photoelectrons from Metals due to a Surface Effect

Expressions are derived for the distribution in total energy of photoelectrons from a metal on the basis of the alternative assumptions concerning the photon absorption process made by DuBridge and by Fowler. The calculations are exact, avoiding the usual approximation that the frequency of the incident light must be near the threshold frequency. Expressions are given not only for the distribution in energy of electrons emitted in all directions but also for the energy distribution as a function of emission angle.

Electrodisintegration ofCu63andMn55

The electrodisintegration of ${\mathrm{Cu}}^{63}$ and ${\mathrm{Mn}}^{55}$ has been investigated for total electron energies from 29.5 Mev to 81.5 Mev by a stacked-foil experiment using the internal electron beam of a synchrotron. The value of $\overline{F}$, which is essentially the ratio of photon induced foil activity to electron induced foil activity, is found to be 8.32\ifmmode\pm\else\textpm\fi{}0.54 at 29.5 Mev, 5.47\ifmmode\pm\else\textpm\fi{}0.36 at 46.5 Mev, 5.31\ifmmode\pm\else\textpm\fi{}0.25 at 63.5 Mev, and 4.97\ifmmode\pm\else\textpm\fi{}0.05 at 81.5 Mev for the ${\mathrm{Cu}}^{63}(e, {e}^{\ensuremath{'}}n){\mathrm{Cu}}^{62}$ reaction. For the ${\mathrm{Mn}}^{55}(e, {e}^{\ensuremath{'}}3n){\mathrm{Mn}}^{52*}$ reaction, which has an effective excitation energy of 42 Mev, $\overline{F}$ is found to be 6.67\ifmmode\pm\else\textpm\fi{}0.41 at 63.5 Mev and 7.43\ifmmode\pm\else\textpm\fi{}0.40 at 81.5 Mev. Upon comparing these values with the theoretical values of $\overline{F}$ for different multipole photon absorption processes, it appears that the resonance peak in the nuclear photon absorption cross section for copper is due to a mixture of 97% of an electric dipole process and 3% of an electric quadrupole process. Nuclear size effects might make the experimental results compatible with a larger proportion of electric quadrupole process. Above the resonance peak, at energies near 42 Mev, the photon absorption appears to be due to either an electric dipole or a magnetic dipole process, but not an electric quadrupole process.

Measurement of Shot Noise in CdS Crystals

The noise power spectrum associated with photoconduction current in CdS crystals with indium electrodes is found to flatten off at low frequencies at a value that corresponds closely to the noise inherent in the photon absorption process itself plus that associated with the random nature of the carrier recombination process. It is found that the noise power is not a unique function of the photoconduction current, but varies as the square of the applied voltage, and linearly with light intensity, as suggested by a simple model not unlike that of the photomultiplier.