Davorka Azinović

The NaZn excimer : blue-green band

Electronically excited NaZn excimers have been produced in a photochemical reaction of Na2(C 1Πu) with Zn(4 1S0). The Na–Zn vapor mixture was prepared by introducing a controlled stream of sodium vapor into zinc vapor generated in a heat‐pipe oven. A new band (bound–free transition) was observed in the region from 450 to 487 nm. Potential curves of the eight lowest electronic states of NaZn were calculated. On the basis of the calculations, the observed emission is interpreted as resulting from the 2 2Π–X 2Σ+ transition. The conditions favorable for the observation of the photochemical reaction are discussed.

Blue-green bands of LiCd

Abstract Excited LiCd molecules are formed in a photochemical reaction of Li2 (C1Πu) molecules with cadmium atoms in the ground state. Bound-free emission of LiCd molecules is observed in the region from 460 to 500 nm, which shows, in contrast to similar systems, a structured continuum with two distinct maxima at 482 and 489 nm. From ab initio SCF MRDCI calculations, augmented by an approximation for the spin-orbit splitting, the observed emission is interpreted as resulting from the 22Π3/2−X2Σ+ 1 2 and the 22Π 1 2 −X2Σ+ 1 2 transitions of LiCd.

Spectral simulation and interpretation of LiZn and LiCd blue-green emission

Excited LiZn and LiCd molecules are produced in a photochemical reaction between Li2(C1Πu) molecules and zinc or cadmium atoms. Changes in shape of the blue-green emission are observed by increasing the total vapor pressure in the heat pipe oven. Quantum mechanical spectral simulations are carried out for the relevant 22Π →X2Σ+ transitions. Both bound-bound and bound-free types of transitions are found to play an important role in the overall blue-green spectra. For high collision frequencies (high total vapor pressure) the simulated spectra show very good agreement with observations if a thermal distribution in the 22Π states is assumed. In this case bound-bound transitions are dominant. The results for low collision frequencies indicate that the nascent distribution is non-Boltzmann and that bound-free transitions are dominant.

PHOTOCHEMICAL PRODUCTION OF KCD EXCIMER BANDS

Abstract The electronically excited KCd 2 2 Π state has been populated in a photochemical reaction of K 2 ( C 1 Π u ) with Cd95 1 S 0 ). The KCd vapor mixture was prepared in a crossed heat-pipe oven. The atom densities of the K and Cd atoms in the vapor mixture were controlled by preparation of the amalgams with different mole fraction ratios of the relevant components. A new diffuse excimer band was observed in the region from 600 to 660 nm. Quantum mechanical spectral simulations for the KCd 2 2 Π → X 2 Σ + transition were performed, using potential energy curves calculated by Czuchaj, Rebentrost, Stoll and Preuss and showed good agreement with experiment. Other KCd transitions observed in different experiments are discussed.

Cross section for the photochemical formation of the NaZn (22Π) excimer

We studied the conditions for the photochemical formation of the NaZn excimer in the excited 22Π state using Na2(21Πu)+Zn→NaZn(22Π)+Na reaction. The Na-Zn vapor mixture was prepared in the heat-pipe oven with the well defined column density and temperature. The Na and Zn atom densities in the vapor mixture were controlled by the preparation of the alloy with different mole fraction ratios of the relevant components in the solid phase. The Na densities were determined from the total absorption coefficient at Na2 X-B and X-A bands. The cross section for photochemical formation of the NaZn in the 22Π state is estimated to be 17·10−16 cm2 for the laser excitation at 308 nm, measured relative to the cross section of 470·10−16 cm2 for collisional energy transfer Na2(21Πu)+Na→Na2(23Πg)+Na published by Mehdizadeh et al. [2].

Ultraviolet and blue NaHg and NaCd excimer bands

We present the current-reversal spectra of the high pressure Na-Hg-Xe and Na-Cd-Xe lamps, from which the specific NaHg and NaCd structured continua have been observed. Detailed analysis revealed the existence of additional structure in the case of NaCd and NaHg blue diffuse bands. In the NaHg case the neighbourhood of the 330 nm sodium line revealed two satellite bands of NaHg origin, but almost no structure around the 330 nm sodium atomic line was found in the case of Na-Cd-Xe discharge lamp.

Observations and spectral simulations of the7Li2 21 Σ u + →X1 Σ g + transition

The7Li2 21 Σu+ →X1 Σg+ electronic transition has a bound-bound and a bound-free part due to the double minimum nature of the upper 21 Σu+ state. We have studied this transition both experimentally and by performing spectral simulations. When inner well was excited the bound-free part at 4525 Å was observed due to the collisions between Li2* and argon. We found that when levels above the barrier are excited the bound-free emission is strongly affected by collisional relaxation of Li2* by Li atoms. Conditions for the observation of the bound-free part are discussed.

Resonance excitation of lithium and radiative collision in Li+Cd system

Using resonance excitation of the lithium 2p atomic level in a lithium-cadmium vapor mixture we observed cadmium atomic transitions from very high levels. Time dependent fluorescence intensity from various lithium and cadmium atomic levels is measured. Solving a system of 11 rate equations simulates the time evolutions of corresponding atom densities in the lithium and cadmium atomic energy levels. From the best fit we estimate rate coefficient for radiative collision Li(2p)+Cd(51S0)+hν670.8 forming Li(2s)+Cd(53P0).

Resonance 2s-2p excitation of lithium in the Li + Cd system

Using the resonance 2s-2p excitation of the Li atom in a lithium-cadmium vapour mixture we observed cadmium atoms excited to very high energy levels such as 6s 3S1, 5d 3DJ and 6p 1P1. As the main excitation process we propose radiative collisions between excited lithium and ground state cadmium atoms followed by an energy-pooling collision between Cd(3PJ) atoms. The temporal evolution of intensities of selected lithium and cadmium atomic lines is simulated using a system of rate equations. We estimated the rate coefficient for the radiative collision Li(2p) + Cd(5 1S0) + hν670.8 nm + ΔE→Li(2s) + Cd(5 3P0), to be 6×10-10 cm3 s-1 at T = 965 K.