With t he aid of new data on wavelengths, intensities, and t he Zeem an effect, t he structural analysis of the first spectrum of rhenium (Re I) has been extended to include 2,764 lines that are explained as transitions among 282 atomic en ergy levels. This analysis accounts for 90 percent of the total observed intensity, alt hough only 64 p ercent of t he t otal number of lines has been classified. From the Zeeman effect, magnetic splittin g fac t ors h ave been derived for 75 percent of the levels, and nearly 40 percent of t hese have been grouped into designated spectral terms ascribed to speci fic configurations of electrons. The normal state of neutral R e atoms is 5d 5 68 2 682», and t he ionization limit is approximately 63530 kaysers or 7.87 electron volts.

The absorption spectra of LiH and LiD have been observed in the near ultraviolet with high dispersion and absorbing path lengths up to 16 meters. A new band system has been found in each molecule involving the ground state and a 1Π excited state. Rotational and vibrational analyses of this system have been carried out and rotational and vibrational constants for the upper state have been determined. The observed breaking off of the rotational structure of the bands of this B1Π—X1Σ+ system has been interpreted as due to predissociation by rotation. With this assumption very accurate dissociation limits of the B1Π state have been obtained. From these dissociation limits the dissociation energies of the three known electronic states of LiH and LiD have been calculated. In particular the dissociation energies (D0) of the ground states of LiH and LiD have been found to be 2.4288 ± 0.0002 ev. and 2.4509 ± 0.0010 ev., respectively.

Articles you may be interested inQuantum theory and collisional propensity rules for rotationally inelastic collisions between polyatomic molecules (NH3 and CO2) and an uncorrugated surface J. Chem. Phys. 89, 790 (1988); 10.1063/1.455202 Collisioninduced transitions between molecular hyperfine levels: Quantum formalism, propensity rules, and experimental study of CaBr(X 2Σ+)+Ar When a mixture of lithium vapor and argon is irradiated with the light from an argon ion laser and the resulting fluorescence of the Li2 B 'IIu-X l~g+ band system is examined under high resolution, a pattern of collision-induced satellite lines is observed to accompany the parent resonance fluorescence series. Under conditions of low pressure these satellite lines originate from single inelastic events which alter the rotational state of the excited Li, molecule. The relative intensities of the satellite lines are found to be markedly different depending on whether the collision-induced transition originates from the upper or lower component of the A doublet of the II state, referred to as c or d, respectively. An increase in J( +LiJ jump) is favored over a decrease (-LiJ) for d->c jumps whereas -LiJ is favored over +LiJ for c->d jumps. On the other hand ±LiJ changes that preserve the character of the A component, i.e., c->c and d->d, occur with nearly equal probability for the same value of LiJ. This behavior has been observed for the satellite lines corresponding to LiJ = ±1, ±2, and in some cases ±3 for (v', J', c, or d) levels (2, 31, c), (3,30, c), (9,38, c), (4,24, d), and (7,61, d) of 'Li2 and (0,45, d) of 6Li 'Li. In 'Li2 only collisional transitions between symmetric or between antisymmetric levels are allowed. For 6Li 7Li, which does not have this symmetry, more satellite lines are observed. However, these additional lines are significantly weaker since the 6Li 7Li molecule is nearly homo nuclear. A simple classical model is suggested which may help to explain the different rotational quantum jump propensities for the two A components.

The fluorescence spectra B lIIu-X l1;g+ of the molecular species 6Li" 6LPLi, and 7Li 2 , excited by the cw lines of the argon ion laser, have been observed and analyzed. Based on a short Birge-Sponer extrapolation of the vibrational levels of the ground state, the dissociation energy for the Li2 molecule has been determined to be D o o=1.026±0.006 eV. This value, combined with the dissociation limit of the upper state determined by Loomis and Nusbaum, proves that there is a hump of about 0.12±0.04 eV above the asymptote of the potential curve of the Li2 B lIIu state. Improved rotational and vibrational constants of the ground state of Li2 have also been obtained. A new technique is described which utilizes collision-induced rota tional transfer to facili ta te the v', J' assignment of the excited levels. INTRODUCTIONThe dissociation energy of the Li2 molecule has been the subject of some controversy for many years. The first determination of its value was made by Wurm 1 as a result of his study of the fluorescence spectrum excited by sunlight, and involved a Birge-Sponer extrapolation from v" = 9. The value obtained (DoO = 1.69 eV) was in rather good agreement with quantummechanical calculations performed by Delbruck 2 at about the same time (1.4 eV).In 1931, Loomis and Nusbaum 3 observed and analyzed the magnetic rotation spectrum of Li2• From a short extrapolation of the vibrational structure of the B III" excited state they obtained a value of Doo= 1.14±0.03 eV, which again was in agreement with new quantum-mechanical calculations (1.09 eV) published by Bartlett and Furry.4 Lewis,5 using a molecular-beam method,6 determined the dissociation energy of Li2 to be Doo= 1.03±0.04 eV. However, the limits of error of his results as well as those of Loomis and Nusbaum were still broad enough that the spectroscopic and thermochemical measurements could be possibly reconciled. The good agreement observed between theoretical and experimental values in the earliest investigations was later shown to be fortuitous. James 7 has pointed out that the theoretical calculations omitted the effect of the antibonding 1s(T" electrons. When this contribution is considered, the best Heitler-London calculations give a value of Doo around 0.3 eV, and only with a variational treatment can this value be improved to 0.5 eV. Detailed configuration interaction calculations by Ishiguro et al. 8 have increased the theoretical value of Doo to 0.77 eV, and only recently Das and Wahl 9 have been able to obtain a value of D o o=0.91 eV by combining the SCF method with superposition of configurations.The best spectroscopic value 3 of Doo was deduced by subtracting the energy of the atomic 2p electron from the dissociation limit of the B III" state. This result depends on the accuracy of the dissociation limit determination and on the assumption that the B III" potential curve does not have a hump at large internuclear distances. Rev. 38, 1615Rev. 38, (1931 .• L. C. Lewis, Z. Physik 69,786 (1931).7 H. M. James, J. Chern. Phys. 2,794 (1934)...