M. M. Hessel

The B1Πu–X1Σg+ band system of the 7Li2 molecule

The absorption and laser induced fluorescence spectra of the B1Πu–X1Σg+ band system of the 7Li2 molecule has been photographed at high resolution (360 000) and high dispersion (0.4 A/mm). Over 14 000 spectral lines have been assigned to this band system for a wide range of rotational quantum numbers (J=0−80) and vibrational quantum numbers (v′=0−13 and v″=0−18). Using a Dunham type analysis, we have obtained the molecular constants for both states and have fitted 8358 nonoverlapping lines with an rms error of 0.012 cm−1. The B1Πu lambda doubling constants, including the centrifugal distortion lambda doublet constant, have been determined. Quantum mechanical potential curves have been generated for this system using a novel variational procedure and Franck–Condon factors for different rotational quantum numbers have been determined over the range of vibrational levels observed. Excellent agreement has been achieved for the centrifugal distortion terms Dv, Hv, and LV which were obtained from the least squar...

Theoretical transition dipole moments and lifetimes for the A 1Σ+u→X Σ+g system of Na2

Multiconfiguration self‐consistent field (MCSCF) calculations have been carried out on the X 1Σ+g, A 1Σ+u, and B 1Πu states of Na2. The calculated potential energy curves are in good agreement with the experimental X and A RKR curves of Hessel and Kusch. Both the A→X and B→X transition moments have been calculated as a function of nuclear separation using MCSCF wavefunctions. These calculations are in excellent agreement with the recent experimental determinations of the B→X transition moment. A values and lifetimes of several A‐state vibrational and rotational levels for the A→X transition have been calculated using the theoretical transition moment and the experimental potential curves of Hessel and Kusch. These again are in excellent agreement with the recently measured lifetimes.

Experimental studies of mercury molecules

Optically excited fluorescence spectra in pure mercury vapor have been studied over the spectral range 240–600 nm for temperatures between 400–1000 K and densities between 5×1016–2×1019 cm−3. Absorption measurements were made over the spectral range 253–334 nm, and both structured and continuum bands were observed. Several types of two photon experiments were also performed in order to probe the excited states of the mercury dimer. In addition, the mercury spectrum from mercury vapor–noble gas mixtures has also been studied for noble gas pressures up to 1 atm.

A theoretical analysis of mercury molecules

A theoretical analysis of experimental observations on bound–free electronic transitions in mercury molecules is presented. Potential curves and A values are derived for these transitions and the possibility of emission from a mercury trimer is also discussed briefly. These data are then used to produce a simple model for an optically pumped 335 nm mercury laser. A table is given which predicts the small signal gain at 335 nm as a function of temperature, density, and the excimer density in the vapor.

The intensity distribution in the Na2 and Li2 A–X bands

The accuracy of the quasistatic or classical Franck–Condon approximation for unresolved bound–bound molecular bands is investigated by comparison with appropriately averaged quantum mechanical calculations. Wavelength‐averaged absorption and stimulated emission cross sections are calculated for the A–X bands of Na2 and Li2, representing low resolution or collision broadened spectra, and comparisons are made with experimental spectra. These A–X bands exhibit a red edge, due to a head of heads or a classical satellite, and a comparison of quantum mechanical, classical, and semiclassical satellite shapes is made. The overall quantum mechanical band shapes agree with the classical calculation, except for approximately periodic band structures and nonclassical behavior at the satellites. The emission spectrum resulting from white light or electron excitation of Na2, is also calculated and compared to that observed in an electrical discharge. Finally, emission spectra of Na2 for thermal distributions at various...

Microwave optical double resonance of X 1Σ+ of NaK

A microwave optical double resonance (MODR) study of the ground state X 1Σ+ is NaK is reported. The ν″ = 0 J = 7→8 and J = 8←9, and ν″4 J = 5←6 rotational transitions were observed as changes in the laser induced photoluminescence intensity with the Ar+ laser coincidences (12–0) band P(8) (4765 A) and (’–4) band Q(5) (4965 A), respectively, of the D 1Π–X 1Σ+ system of NaK. The improvement in sensitivity of the MODR technique over traditional microwave spectroscopy is discussed. Improved Dunham coefficients for the X 1Σ+ state are obtained by a weighted merged fit of the previous optical data with the three transitions obtained in the present work.

Analysis of the decay of molecular fluorescence in optically excited mercury vapor

The decay of the 485 and 335 nm molecular fluorescence bands in optically excited mercury vapor is studied. A 10 nsec laser pulse at 256 nm is used to excite the vapor and the subsequent fluorescence intensity between 1 and 2000 μsec was recorded for each band. At late times following the laser pulse, both bands decay at the same exponential rate. This exponential decay coefficient was measured as a function of gas density from 1017 to 1019 cm−3 and as a function of temperature from 473 to 1048 °K. These decay data, as well as data on the relative intensities of the two bands, are analyzed in terms of a simple kinetic model for the mercury vapor system and various kinetic rates are determined. Some decay rates for the 6 3P atomic manifold are also obtained and compared with previous measurements.

Relaxation of the mercury 6 3P0 and 6 3P1 states

The relaxation of 6 3P0 mercury atoms excited by a laser pulse was measured for densities ranging from 2×1017 to 8×1018 cm−3. The decay of the 253.7 nm resonance line was also measured for densities ranging from 5×1016 to 1018 cm −3. The decay coefficients were analyzed to yield rate coefficients for three body molecular formation, the 3P1→3P0 collision rate and a collisional quenching rate for the 3P0 state. Small loss rates due to diffusion and radiation were also observed and found to be consistent with theoretical estimates of these quantities.

Two‐Metal Heat‐Pipe Oven: Operation, Dynamics, and Use in Spectroscopic Investigations

Two different metals in a heat‐pipe oven will form separate metallic‐vapor zones. These zones can be moved so that in a crossed heat‐pipe oven, spectroscopic studies of intermetallic molecules can be made at the interface between the two zones. We describe the operation and construction of the two‐metal heat‐pipe oven as well as a laser technique that can be used to study some of the dynamics of the heat pipe.

Relaxation of the first excited 1u state of Hg2

The decay of the 335 nm Hg2 fluorescence band was measured with 1 nsec time resolution for the first 200 nsec following optical excitation by a 10 nsec laser pulse. Measurements of the decay rates for various wavelengths in this band were used to analyze the relaxation of the vibrational levels in the 1u state. It was found that the lower vibrational levels quickly reach a Boltzmann distribution described by an effective temperature Teff. This effective temperature then decreases with time, asymptotically approaching the gas temperature. Comparison of these data with a model calculation by Montroll and Shuler yields a transition rate of 5.2×10−11 cm3 sec−1 for the transition between the two lowest vibrational states. Analysis of the relaxation for higher vibrational levels gave a value of 2.7×10−10 cm3 sec−1 for the 1u→0−g transition rate. Since no mercury trimers have been formed at these early times, the 485 nm fluorescence band is not present. It was therefore possible to evaluate the repulsive wall of...