Collision-Induced Dipole Transitions Research Articles

Collision-induced dipole transitions and collisional broadening of quadrupole transitions

Collision-induced dipole transitions and collisional broadening in the wing of $\mathrm{Cs}(5D)$ due to mixing with $\mathrm{Cs}(7S)$ and $\mathrm{Cs}(6P)$ are studied using two-photon resonance ionization spectroscopy. From the structure of the line shape, we measured the van der Waals well of the ground state without performing a temperature study or using the calculated potential curves, and from the absolute yield we measured the induced-dipole oscillator strength as a function of the internuclear separations at large separations. The results are compared with theoretical calculations.

Collision-Induced Dipole Transitions Associated with High-Lying States. III. Comparison with Theory for Rubidium in Xenon

Photoabsorption method has been applied to Rb-Xe system to observe collision-induced dipole (CID) transitions 5 s - n s ( n =10 and 11), - n d ( n =8 to 16) and - n q ( n =7 to 15), where q stands for the manifold states or l ≥3. Measured shift is almost constant (≃14 cm -1 ) for 5 s - n d , whereas it decreases from 41 to 10 cm -1 for 5 s - n q as n increases. Measured effective oscillator strength per unit xenon density f CID /[Xe] (10 -27 cm 3 ) decreases from 35 to 2 for 5 s - n d and from 64 to 34 for - n q as n increases. The f CID /[Xe] values of rubidium are quantitatively explained by the theory that takes account of the energy dependence of the s -wave amplitude for electron-xenon scattering.

Collision-Induced Dipole Transitions Associated with High-Lying States. II. Experimental and Theoretical Studies of Calcium in Rare Gases

More than 20 collision-induced dirole (CID) transitions (4 s 2 -4 s n s with 7 ≤ n ≤9, -4 s n d with 5 ≤ n ≤12, -4 s n f with 4 ≤ n ≤8, etc.) have been observed in the absorption spectrum of calcium below 2400 A in the presence of xenon or krypton. Some of them have been also observed in the presence of argon, neon or helium. The measured shifts and the effective oscillator strengths show a close correlation with low-energy-electron-scattering parameters of the rare-gas atoms. Present theoretical calculation of the effective oscillator strengths for 4 s 2 -4 s n d (8 ≤ n ≤12) reproduces the dependence of the measured oscillator strengths on the scattering lengths of the rare-gas atoms and on the effective principal quantum numbers of the upper D levels, but the calculation gives larger values by a factor of about 4 than the experiment.

Collision-Induced Dipole Transitions Associated with High-Lying States. I. Absorption Studies of Barium in Rare Gases

Absorption method has been applied to observe the collision-induced dipole transitions associated with the optically forbidden transitions 6 s 2 1 S 0 -6 p 2 1 D 2 , -6 s 9 d 1 D 2 , -6 s 10 d 1 D 2 , and -5 d 8 p 1 D 2 of barium in argon, krypton or xenon atmosphere. The effective oscillator strength per unit rare-gas density is obtained to be, e.g. , for 6 s 2 -6 s 9 d , 3.6×10 -24 , 2.0×10 -23 , and 5.8×10 -23 cm 3 for argon, krypton, and xenon, respectively. A correlation is found between the effective oscillator strength and the scattering length of the rare-gas atoms for electrons. This is explained from a model in which an adjacent P state mixes into the D state due to the interaction potential between the loosely-bound valence electron and the rare-gas atom.

Collision-Induced Dipole Transitions Associated with Rydberg States of Rubidium in Xenon

For rubidium atom perturbed by xenon, absorption measurements have been made to observe collision-incuded dipole transitions 5 s - n s ( n =10 and 11), - n d (8≤ n ≤16) and - n q (7≤ n ≤15), where q stands for the manifold states of l ≥3. The n -dependence of the measured effective oscillator strengths is reproduced well by the approximate calculation using a simple model based on the interaction of a Rydberg electron with a xenon atom, although the calculation gives larger values than the experiment by a factor of about 4.

Collision-Induced Dipole Transitions Associated with High-Lying States of Calcium in Rare Gases

Several collision-induced dipole transitions have been observed in the absorption spectra below 2400 A of calcium perturbed by rare gases. The obtained effective oscillator strengths per unit rare gas density are found to correlate with low-energy electron scattering cross sections on the rare-gas atoms.

Observations of the collision-induced dipole transitions and of a quadrupole transition for barium in krypton

For Ba perturbed by Kr, collision-induced dipole transitions 6 s 21 S 0 – 6 snd 1 D 2 (8⩽ n⩽10) have been observed. The effective oscillator strength per unit Kr density was found to be 1.8–1.0 x 10 -23 cm 3. For the electric-quadrupole transition 6 s 21 S 0 -6 s6 d 1 D 2, the oscillator strength is (2.0±0.4) x 10 -6.

Emission cross sections of the A 1Π state of NO +

Emission cross sections have been measured for the production of the A 1Π-X 1Σ + bands of NO + in the vacuum ultraviolet for 0.1–3 keV electrons incident on NO. The energy dependence of the cross sections was analysed by means of the Bethe-Born approximation. The relevant ionization process was found to be (mainly) due to collision-induced dipole transitions. The variation of the electronic transition moment R e for the A 1Π-X 1Σ + transitions was determined from cross-section ratios and known Franck-Condon factors. In our range of ν centroids | R e| 2 varied as much as a factor of 2.

Emission cross sections of the A 2Π and B 2Σ + states of CO +

Absolute emission cross sections for production of radiation of the A 2Π and B 2Σ + states of CO + have been determined for 0.05–5 keV electrons incident on CO. The results are analyzed by means of the Bethe approximation. A strong contribution from collision-induced dipole transitions is found in the excitation processes. Cross sections for formation of the A 2Π, B 2Σ + and X 2Σ + states have been calculated. In some cases the variation of the electronic transition matrix element R e could be determined from ratios of cross sections for specified vibrational transitions. The apparent cross sections for emission of the A 2Π−X 2Σ + band system were found to be dependent both on the gas pressure and the electron current used. These effects are connected with an excitation transfer process and a pressure effect found in lifetime measurements. A comparison is made with existing proton- and photon- impact data and also with electron data of N 2.

Emission cross sections of the first negative band system of N 2 by electron impact

Cross sections have been measured for the emission of the First Negative Band system of N 2 when excited by electrons in the energy range of 0.1 to 6 keV. In particular the v“ progressions with the v' = 0 and 1 levels have been investigated. The emission cross sections can be analyzed by application of the Bethe-Born approximation. A relatively strong contribution from collision-induced dipole transitions is found in the excitation process. The energy behaviour of all vibrations is the same. The total emission cross sections of both v” progressions account for 12.5% of the total ionization cross sections of N 2. Comparison is made with existing electron, proton and photon impact data.

Gross- and Partial-Ionization Cross Sections for Electrons on Water Vapor in the Energy Range 0.1–20 keV

Measurements have been made on the gross-ionization cross sections for 0.1–20-keV electrons on water vapor at pressures of about 3×10−4 torr. The results are compared with the cross sections of H2 and O2. Within the experimental error of 15% we found no deviations from the additivity rule. The energy dependence of the cross section satisfies the Bethe—Fano—Platzman relation for collision-induced dipole transitions at energies exceeding 400 eV. A comparison is made with photoionization and inelastic electron-scattering cross sections. Some results are given on the partial cross sections for the production of fragment ions for 0.02–2-keV electrons on water vapor.