W. Kedzierski

Production of ground state OH following electron impact on H2O

Laser-induced fluorescence (LIF) measurements of OH(X 2Π) production following electron impact on water have been carried out over an energy range from threshold to 300 eV. Data have been made absolute using existing measurements of OH(X) production via dissociative attachment. The cross section reaches a maximum value of 2.1×10−16 cm2 at an energy of 75 eV. Dipole-allowed processes are shown to dominate the production of OH(X) particularly via the A(1B1) repulsive state, though significant population of higher rotational levels is demonstrated, indicating the relevance of other channels as in photodissociation.

Isotope effects in the electron impact break-up of water

Total fragmentation of and has been studied as a function of incident energy over the range from threshold to 325 eV. A small subset of possible dissociation channels has been selected by making use of a novel solid xenon matrix detector which is selectively sensitive to metastable atoms. O-fragment kinetic energies and appearance potentials have been measured and significant isotopic effects are observed. Within the errors of the measurements the cross section for production from is the same as that from . The cross sections reach a maximum value of at 100 eV incident electron energy.

Laser spectroscopy of the 1Σ+u (4 1P) and 3Πu (4 3P) states in Zn2

Abstract The 0 + u (4 1 P) state of Zn 2 was excited near the crossing of the 1 Σ + u (4 1 P) and 3 Π u (4 3 P) states, using pump and probe methods with time resolution. A structured excitation spectrum was observed in the 530–570 nm region and is ascribed to the 3 Π u (4 3 P)← 3 Π g (4 3 P) vibronic transitions. A fluorescence spectrum which was emitted in the 250–306 nm region is believed to arise from the 1 Σ + u →X 1 Σ + g bound—free decay. It consists of a “Condon internal diffraction pattern” whose profile suggests that it was emitted from a high vibrational level ( v ′ = 19) of the 1 Σ + u state.

The rotationally resolved G0+u ← A0+g electronic spectrum of the (202Hg)2 excimer

Abstract Isotopically pure 202 Hg vapor, contained in a quartz cell, was irradiated with frequency-doubled 5140 A output from an Ar + laser, which caused the formation of Hg 2 A0 ± g excimer molecules by photoassociation. Simultaneous probe radiation from a ring dye laser scanned over a range 5400–6000 A, produced the G0 + u ← A0 + g excitation spectrum which consists of several hundred well-resolved rotational components that have not been previously observed. Two vibronic bands were subjected to a rotational analysis which yielded spectroscopic constants that are compared with some previously reported values.

Laser-induced 1Σ+u ← 3Πg excitation spectrum of Zn2

Abstract A structured excitation spectrum of Zn2 in the 420–470 nm region was registered in zinc vapor subjected to pump-and-probe excitation as the emitted bound—free fluorescence was monitored at 274 nm. The excitation and fluorescence spectra were interpreted as due to transitions involving the 1Σ+u (5 1S), 3Πg (4 3P), and X1Σ+g (4 1S0) states. An analysis of the vibrational structure yielded vibrational constants and relative energies for the 1Σ+u and 3Πg states.

Laser spectroscopy of the 3Σ+u(4 3P, 4 3P) state of Zn2

Abstract The doubly-excited 3Σ+u (4 3P, 4 3P) state of Zn2 was populated using pump and probe methods with time resolution. Structured excitation and fluorescence spectra were observed in the 300–330 nm region and are ascribed to 3Σ+u (4 3P, 4 3P)↔3Πg(4 3P) vibronic transitions, with partial resolution of the fine structure. An analysis of the spectra yielded the vibrational frequencies, relative energy, and relative equilibrium internuclear separations for the 3Σ+u and 3Πg states. The Zn2 excitation and fluorescence spectra contained a number of atomic lines whose origin was probed in a subsidiary experiment.

Laser-induced fluorescence from the 3Πu(43D) state of Zn2

Abstract The 3 Π u (4 3 D) state of Zn 2 was excited using pump and probe methods with time resolution. Structured excitation and fluorescence spectra were observed in the 325–360 nm region and are ascribed to 3 Π u (4 3 D)↔ 3 Π g (4 3 P) vibronic transitions. An analysis of the vibrational band structures yielded the vibrational frequencies, relative energy and relative equilibrium internuclear separations for the 3 Π u and 3 Π g states.

Laser-induced fluorescence of the Zn 2 excimer

Pump-and-probe methods of laser spectroscopy with time resolution were used to study fluorescence and excitation spectra arising from transitions involving the (1) product operator(u)(4(1)P), (3) product operator(g)(4(3)P), and X(1)Sigma(+)(g)(4(1)S) states for the Zn(2) excimer. An analysis of the vibrational bands yielded vibrational constants, relative energies, and relative internuclear separations for the (1) product operator(u) and (3) product operator(g) states.

Electron impact dissociation of OCS

A special matrix isolation detector, sensitive to S(1S0), has been used to study the dissociation of OCS into this fragment over an electron energy range from threshold to 400 eV. The maximum cross section occurs at an impact energy of 55 eV and has been measured to be 3.3×10-17 cm2. Time of flight spectroscopy has been used to monitor fragment kinetic energies. Optically allowed processes are observed to dominate the dissociation. Striking similarities between electron and 157 nm photon dissociation have been noted.

A Fizeau wavemeter with single-mode optical fibre coupling

An improved Fizeau wavemeter for CW and pulsed laser wavelength measurements was developed, incorporating single-mode optical fibre coupling. The whole optical system is enclosed in an evacuated chamber and the optical fibre acts as a spatial filter, resulting in an improved performance and increased simplicity of alignment and operation. Wavelength measurements have been performed with an accuracy better than 1 part in 106 for CW lasers and 2 parts in 106 for pulsed lasers.