Daniel J. Kligler

Nonlinear optical processes in atoms and molecules using rare-gas halide lasers

The use of nonlinear optical processes expands the flexibility of excimer systems in the study of a wide range of atomic and molecular phenomena and materials. These mechanisms have already allowed for the selective excitation of states in the 10 to 20 eV range involving bound state excitation, ionization, and molecular dissociation. Specific examples involving the electronic excitation of H 2 , Kr, and Xe, the production of Xe+for the analysis of the molecular properties of XeF*, and nonlinear photodissociation of N 2 O and OCS are discussed.

Energy ordering of the excited states of XeF

Ar/Xe/NF3 mixtures were excited by the focused beam from an ArF (193 nm) laser. Xe+ ions are produced by two‐photon ionization, the electrons attach to make F−, and the ions recombine to make XeF*. Radiation is observed in the XeF(B 1/2) →XeF(X 1/2) bands near 351 nm and in the broader XeF(C 3/2) →XeF(A 3/2) band near 460 nm. At low background gas pressure, mostly B‐X uv emission is observed. As the argon pressure is increased to 1000 Torr, the visible/uv band intensity ratio increases to about 3 to 1. We conclude from these results that the C (3/2) state lies 700±70 cm−1 below the B (1/2) state. This conclusion should have a significant impact on our understanding of the fluorescence yields and laser performance of e‐beam‐excited XeF.

Photolytic production of S(1S) from OCS by two‐quantum and vibrationally dependent mechanisms

Studies of photolytic production of S(1S) atoms by two‐photon dissociation of OCS at 193 nm are reported. The excited sulfur atoms are detected by observation of the collisionally‐induced XeS(2 1Σ+ →1 1Σ+) emission near the S(1S→1D) atomic line at 773 nm. The measured OCS two‐quantum absorption cross section is in accord with theoretical estimates based on previous established spectroscopic data. In addition, it is found that excitation of the OCS (ν2) bending vibration by CO2 laser irradiation causes the S(1S) yield to be considerably enhanced. The experimental data obtained indicate the presence of vibrational mode specificity in the mechanism of photolytic enhancement. Vibrationally dependent quenching arising from OCS† +S(1S) collisions is also observed. The mechanisms of vibrational enhancement are discussed in relation to their general applicability for photolytic production of electronically excited species.

XeO* production through collisional electronic energy transfer from two-photon excited Xe atoms

The observation of electronic energy transfer to XeO(1Σ+) from xenon atoms excited by two‐photon absorption is reported. Electronically excited xenon atoms in the 5p56p configuration are produced through two‐photon excitation at 248.4 nm (KrF*). Subsequent energy transfer from excited rare‐gas atoms to N2O leads to the appearance of XeO(1Σ+), which is identified by the detection of its characteristic green emission band. These measurements are in accord with estimates of the relevant two‐photon amplitudes for Xe and N2O. Kinetic studies utilizing these techniques provide a flexible method for the study of selective excitation and energy transfer in a wide class of atomic and molecular materials.

ArF laser photolysis of OCSe. I. Se(1S) quenching processes

Quenching rates for Se(1S) and Se*2 by OCSe have been measured using ArF laser photolysis of OCSe at 193 nm for the generation of Se(1S) atoms and the reactive mechanism Se(1S)+OCSe→Se*2+ CO as the source of Se*2. The experimentally determined quenching rates are (1.6±0.4) ×10−10 and 4.6×10−11 cm3 molecule−1 sec−1 for the processes OCSe+Se(1S) and OCSe+Se*2, respectively. Evidence is presented which demonstrates that the Se*2 is formed initially in a state other than the strongly radiating B 3Σ−u level.