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A drift tube mass spectrometer coupled with a continuous laser photon source has been used to study photodissociation of thermal energy positive ion clusters. Absolute photodissociation cross sections have been measured for O2 +(H2O)1,2, O2 +(O2), O2 +(CO2), and H+(H2O)n=1–4 at room temperature and for low field conditions (10 or 14.3×10−21 V m2). Photon wavelengths ranging from 676.4 to 454.5 nm were studied. The H+(H2O)n=1–4 were found to have small or zero cross sections; upper limits on their cross sections were obtained. The O2 +(H2O) and O2+(CO2) cross sections behave similarly over part of the photon energy range. Near 2.60 eV both ions have cross sections approaching 6×10−22 m2. The photodissociation of O2 +(CO2) produces a CO2 + photofragment. From the appearance of this fragment an upper bound on the dissociation energy of O2 +(CO2) was placed at 0.46 eV.

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The laser excited fluorescence spectrum of NCO from an atmospheric pressure CH4/N2O/N2 flame is reinvestigated with a more sensitive apparatus than used previously. The NCO is pumped from the X 2Π (1,01,0) level to the A 2Σ+ (0, 00, 0) level. Emissions to (0, 01, 0)2Π, (1, 01, 0)2Π, (0, 01, 1)2Π, and (0, 10, 0)2Σ+ in the X state are observed. The previous tentative assignment of pumping transition as Q231 is confirmed. The confirmation of pumping transition solidifies our earlier interpretation that excited state spin relaxation in the flame is much faster than electronic quenching. In addition, analysis of the fluorescence spectra yields the first reported constants for the X(1, 01, 0)2Π level and spin splitting for X(0, 01, 1)2Π level in the gas phase.

Laser excited fluorescence of the NCO radical has been obtained using discrete prism selected lines of an argon ion laser pump source. To our knowledge this is the first time NCO fluorescence has been obtained in a flame environment. NCO was formed in a slightly rich atmospheric pressure CH4/N2O flame. This flame was placed inside the extended cavity of the argon laser to take advantage of the much higher light intensity levels. All of the available laser lines pump vibrational hot bands of the NCO A 2Σ+ ← X 2Π system. The 4658 Å line appears to be the most useful for probing NCO densities. This line pumps in the A 2Σ+(0,00,0) ← X 2Π (1,01,0) vibrational band. NCO is pumped to N′ = 31 by this line, probably via the Q231 transition although the R230 and P232 transitions could not be ruled out in the present analysis. The 4658 Å line was used to determine a relative NCO density profile through the reaction zone of a CH4/N2O flame. Profiles of C2, CN, and temperature were also obtained in this flame and are compared with the NCO profile. A lower limit of approximately 3×1014 cm−3 was placed on the peak NCO density in the flame. Attempts to find NCO or CN fluorescence in a CH4/air flame failed indicating probable differences in nitrogen chemistry for the two flames.