Einstein Coefficients For Spontaneous Emission Research Articles

Ab initio prediction of the vibration spectra of the deuterated species of H +3

Ab initio calculated values of the most intense vibration band centers and electric-dipole Einstein coefficients for spontaneous emission are reported for the molecular ions D + 3, H 2D +, and HD + 2. The eigenenergies and wavefunctions for nuclear motion were obtained by a superposition of configurations consisting of products of three eigenfunctions of model one-dimensional hamiltonians. The Born-Oppenheimer potential-energy and electric-dipole-moment surfaces were obtained from an electronic configuration-interaction calculation with near-Hartree-Fock limit orbitals expanded in a floating gaussian basis.

Brightness and Temporal Variation of Radio Emission from Galactic OH

THE recent interferometric observations of the angular sizes of OH radio sources1–3, which imply minimum brightness temperatures of between 106 and 1011 °K, remove any theoretical difficulty in accepting the temporal variations of intensity that the radio astronomy group at Berkeley claim to have detected4. The time constant for a variation of intensity may, in the absence of a rigorous solution of the equations of transfer and population densities for even a simple model, be estimated in two ways that lead to the same result. A simplified equation of transfer for any one of the four radio frequency lines is where i denotes the upper level of the Λ-doublet as split by hyperfine interaction, j denotes the lower level, Iij is the intensity of the radiation, vij is the difference of the number of densities in the two levels, c is the velocity of light and (Aij is the Einstein coefficient for spontaneous emission and δv the width of the line.) This equation of transfer incorporates a number of approximations which seem entirely justified in view of the very high intensity of the radiation, namely, that the rates of spontaneous emission and of non-radiative creation and destruction of excited states can be ignored in comparison with the rate of stimulated emission, and that the radiation is propagating in one direction only. The four equations for the four radio frequency lines are coupled through four simultaneous equations for the rates of change of the populations. It has not so far been possible to solve the eight equations except for very artificial cases. If it can be assumed that there are circumstances in which ∂Iij/∂x is dominated by the other two terms in the equation of transfer, the time constant τ would be

Study of Electronically Excited Iodine Atoms I(52P1/2) by Time Resolved Emission

Donovan and Husain1–7 have recently carried out a number of investigations on electronically excited iodine and bromine atoms, I(52P1/2) and Br(42P1/2), by kinetic spectroscopy in absorption in the vacuum ultra-violet after flash photolysis of a number of gaseous halides. The long mean radiative life-times of these excited atoms8 arising out of the electric dipole forbidden transitions to the ground states, I(52P3/2) and Br(42P3/2), have facilitated such studies in absorption. This communication describes the study of the time resolved emission I(52P1/2) → I(52P3/2) + hv (1.315μ) following the flash photolysis of gaseous trifluoroiodomethane (CF3I), monitored by means of a lead sulphide photoconductive cell placed at the exit slit of a high aperture grating monochromator (Bausch and Lomb, f 4.4) and displayed on the screen of an oscilloscope. The concentrations of excited iodine atoms produced on photolysis2 are sufficiently high to overcome the low value of the Einstein coefficient for spontaneous emission, and adequate intensities are thus obtained. A typical trace for the decay of the emission is shown in Fig. 1. The decay is slower for increasing pressures of argon in accordance with a process primarily controlled by diffusion to the walls of the reaction vessel2–4.