Knowledge Bank

In this work, a tunable difference frequency laser system is employed to obtain high quality, Doppler-limited infrared spectra of transient molecular radicals generated by excimer laser photolysis, and molecular ions produced in an AC glow discharge. The response time of the high resolution, flash-kinetic ir spectrometer is $\lesssim 100$ nsec, with an absorption sensitivity of $\lesssim 0.5\%$ over a 100 cm pathlength, permitting detailed spectroscopic, kinetic, and photofragmentation studies of a wide variety of transient radicals. Data and analysis are presented on the $\nu 1$ and $\nu 3$ CH stretching spectra of singlet methylene over the region $2600-3050cm-1$. Strong interaction between the singlet and ground state triplet manifold is indicated by significant perturbations in the spectrum, and can be sensitively observed by magnetic modulation of the triplet coupled states. For obtaining molecular ion absorption spectra in an AC glow discharge, velocity modulation techniques are employed. By dual beam subtraction of laser amplitude noise, near shot noise sensitivity limits of $\lesssim 10-6absorbance/Hz1/2$ have been achieved. Data is presented on the $\nu 1$ DN stretching mode in $DNN+$; transitions out to $J=20$ in both P and R branch are observed for $(1000)\leftarrow (0000)$ and the hot band $(1110)\leftarrow (0110)$. Rotational constants for ground ground and excited states, vibrational frequencies, and $\ell$-type doubling constants for the $\nu 2$ excited states are reported. Rotational state distributions appear equilibrated in the liquid nitrogen cooled discharge and correspond to a 190 K temperature.