P. Luc

Comprehensive analysis of the A–X spectrum of I2: An application of near‐dissociation theory

High resolution absorption spectra of the A 3Π1u–X 1Σ+g system of I2, consisting of some 9552 lines of some 79 bands spanning the vibrational range v′=0–35 and v″=3–17, have been recorded and analyzed. A fit to them which uses the previously determined accurate molecular constants for the X 1Σ+g state yields an accurate new set of molecular constants for the A state, including the Λ doubling constants. The A‐state vibrational and inertial rotational constants, as well as mechanically consistent centrifugal distortion constants, are represented by near‐dissociation expansions, yielding an accurate representation of the experimental data which also provides a reliable global representation of all observed and unobserved vibration–rotation levels of this state.

Rotational analysis of the 5350 Å band of iodine by means of Fourier transform spectroscopy

Abstract We have recorded the 5350 A (30, 0) band of the iodine spectrum with high resolution by means of Fourier transform spectroscopy. The rotational lines in the P and R branches were measured to J = 165 with reference to uranium standards emitted by a hollow cathode. The differences between the two sets of measurements were less than 0.001 cm −1 , and the standard deviation between the observed wavenumbers and those calculated with the spectroscopic constants B v , D v , and H v is 0.0007 cm −1 . The precision reached is an order of magnitude greater than in previously published data, and the constants H v of the iodine absorption spectrum have been determined for the first time. This work shows that the use of Fourier transform spectroscopy is particularly powerful for molecular absorption studies in the visible region where, although the multiplex gain is lost, the throughput gain remains, and this enables the performance to approach that achieved in the infrared. This method can be expected to open up not only significant new spectroscopic experiments, but it also allows a complete high-precision remeasurement of the existing molecular spectra in the visible and uv (electronic rotational-vibrational transitions).

Assignments of several groups of iodine (I2) lines in the B-X system

Abstract The spectra obtained by means of Fourier spectroscopy and the assignments of the B-X lines of I2 in the vicinity of two argon ion laser lines (5145 and 5287 A), three krypton ion laser lines (5208, 5308, and 5683 A), and one HeNe laser line (6119 A) are given. A detailed comparison, in the vicinity of the argon ion laser line (5145 A), between the iodine wavenumbers calculated by means of the two sets of molecular constants previously published [Wei and Tellinghuisen, J. Mol. Spectrosc. 50, 317–332 (1974); Barrow and Yee, J. C. S. Faraday II. 69, 684–700 (1973)] with those calculated from Fourier spectroscopy data, is presented.

Use of calculated centrifugal distortion constants (Dν, Hν, Lν and Mν) in the analysis of the B ← X system of I2

Abstract Fourier spectroscopy measurements of 14 703 lines from the B - X band system of I 2 are analyzed using centrifugal distortion constants calculated from RKR curves by the perturbation theory method of Hutson [ J. Phys. B 14, 851–857 (1981)]. Only vibrational and rotational constants are varied in the least-squares fits, with the centrifugal distortion constants fixed at the calculated values. The fit obtained in the present work is as good as when the centrifugal distortion constants are treated as independent parameters, but the molecular constants obtained are physically more meaningful because the statistical correlation between parameters is reduced. The analysis includes B -state vibrational levels up to v ′ = 72, which is bound by only 0.5% of the well depth; the method used for calculating centrifugal distortion constants remains reliable even this close to dissociation. It is found that centrifugal distortion constants up to fifth order make significant contributions to the observed line positions.

Rotational analysis of the 7390- and 7937-Å bands of NO2 by means of Fourier transform spectroscopy

Abstract We have extended to higher N and to Ka = 3 and 4 the rotational analysis of the 7390-A band of NO2 performed by K. E. Hallin and A. J. Merer (Canad. J. Phys.55, 2101–2112 (1977)). The lines belong to a perturbed parallel band for which Hallin and others have proposed the vibrational assignment (2 13 1)-(0 0 0) within the electronic ground state. These authors presumed that this band borrows its intensity through a vibronic coupling (spin-orbit and/or Coriolis coupling) from the stronger (0 2 0)-(0 0 0) band of the A - X electronic system at 7460 A. We have observed about 900 transitions belonging to the Ka = 0, 1, 2, 3, 4 subbands of the (2 13 1)-(0 0 0) band for N values going up to about 23, and 300 lines of the “hot” band (2 13 1)-(0 1 0). We have also looked for spin-orbit-induced transitions and we have detected about 400 transitions with ΔN ≠ ΔJ. Among them ΔN = ±2 transitions with ΔKa = 0 or ± 2 have been observed, indicating that N and Ka are no longer good quantum numbers, and demonstrating clearly the existence of rovibronic interactions perturbing the upper levels of the transitions.

Excitation Spectrum of I2 Induced by Laser Radiation Near the Dissociation Limit of the B–State

The study of the excitation spectrum of I2 induced by laser radiation near the dissociation limit of the B state enables us to determine the molecular constants of the vibrational levels v′ = 78, 79 and 80; the latest being situated only 1.6 cm−1 from the dissociation limit. The molecular constants are now in good agreement with theoretical predictions. Revised values of the dissociation limits of the B and X state are proposed: they are 20043.176 ± 0.016 and 12440.200 ± 0.020 cm−1 respectively. The excitation spectrum from 20022 to 20039.5 cm−1 is entirely reproduced, together with the assignments and the wavenumbers of all observed lines, principally for calibration purposes.

Reexamination of the I2 spectrum near the B(3Π0u+) state dissociation limit

Abstract The disagreement of Danyluk and Kings ( Chem. Phys. 25 , 343 (1977)) rotational constants for levels lying near the dissociation limit of B -state I 2 with the mechanical behavior predicted by near-dissociation theory is investigated. The discrepancies are shown to be much too large to be explained by either the neglect of centrifugal distortion effects in the original analysis or by rotational or spin-rotation coupling to a nearby repulsive 1 u state. These differences are therefore attributed to experimental error, a conclusion which is confirmed by more recent experimental results. A reanalysis of the best available data for levels near the dissociation limit of B -state I 2 then yields improved values for the B -state dissociation limit D = 20 043.16 (±0.02) cm −1 of the vibrational index at dissociation v D = 87.32 (±0.04) and of the long-range potential constant C 5 = 2.88 (±0.03) × 10 5 cm −1 A 5 . This in turn implies a slightly improved ground-state dissociation energy of D 0 = 12 440.18 (±0.02) cm −1 .

Displacements Isotopiques Relatifs et Moments Quadrupolaires Intrinseques des Isotopes du Plutonium

Extensive isotope shifts measurements in the 3910-9160 A region of the plutonium spectrum were made. This enables us to determine with precision the value of the Relative Isotope Shift (R.I.S.) between the 244-242 and 242-240 couples of isotopes. The value found for the R.I.S. is 1.03 ± 0.02. Based on the optical R.I.S. of the plutonium isotopes (from 238 to 244) the inherent quadrupole moments of the odd isotopes were determined, using the known values of the quadrupole moments of the even isotopes (deduced from Coulomb excitation). They were found to be respectively equal (in barns) to: Q239 = 11.3 ± 1.0, Q241 = 11.5 ± 0.5, Q243 = 11.6 ± 0.5.

An optical-optical double resonance experiment in LiH molecules: lifetime measurements in the C state.

An optical-optical double resonance sub-Doppler experiment is used to measure short nonradiative lifetimes in the C (1)Sigma(+) state of LiH. These lifetimes are expected to result from the strong electronic interaction between the C (1)Sigma(+) state and the continuum of the A (1)Sigma(+) state and to vary with the vibrational quantum number, from nanoseconds to milliseconds. The experimental setup combines a molecular beam of LiH, a first cw laser beam locked to a given A-X absorption line, and a second cw laser beam scanned over C-A absorption profiles. Analysis of these absorption profiles in terms of Voigt profiles shows that their Lorentzian components significantly vary with the vibrational quantum numbers of the C state. Nonradiative decay rates deduced this way are systematically larger than the calculated ones but their variations are similar. Coherent saturation effects cannot be invoked to explain this discrepancy.

Theoretical interpretation of hyperfine structures in doubly-excited configurations 4f105d6s6p and 4f105d26s and new energy levels in neutral holmium (Ho I)

The configuration 4f105d6s6p of Ho I is studied theoretically. Slater and spin-orbit parameters are determined from 60 energy levels and hyperfine one-electron parameters are derived from magnetic dipole A and electric quadrupole B constants formerly determined in the analysis of Fourier transform emission spectra. A similar study of 4f105d26s is performed. New energy levels are found in analyzing the visible spectrum of holmium, including an excited level of the ground configuration 4f116s2 4F9/2 at 13094 cm?1, and some of the lowest levels of 4f116s6d and 4f116s6d and 4f105d26p.