# DOUBLE RESONANCE STUDIES OF COLLISIONAL ENERGY TRANSFER IN CH$_2$

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 Title: DOUBLE RESONANCE STUDIES OF COLLISIONAL ENERGY TRANSFER IN CH$_2$ Creators: Kim, Yangsoo; Komissarov, Anatoly V.; Hall, Gregory E.; Sears, Trevor J. Issue Date: 2005 Publisher: Ohio State University Abstract: \maketitle We have studied rotational energy transfer byoptical-optical double resonance methods in order to understand the close connection between rotational energy transfer and the mixed-state mechanism of intersystem crossing. Singlet CH$_2$ is produced by 308 nm photolysis of CH$_2$CO. After thermalization of the rotational and translational distribution, a bleaching tunable dye laser pulse depletes the population of a selected rotational level of singlet CH$_2$ while the population of the same (in saturation recovery mode) or a different (in saturation transfer mode) singlet CH$_2$ rotational level is monitored with FM absorption spectroscopy on a different vibrational band of the $\tilde{b}-\tilde{a}$ system. The bleaching laser is blocked and unblocked to record a reference and a bleached transient waveform. The difference of the two signals as a fraction of the reference signal is the saturation recovery signal, which is found to follow a single exponential decay to a final value closed to half of the initial thermal Boltzmann fraction of the population in the bleached level. The rate coefficients for saturation recovery by collision with CH$_2$CO and He are $1.6 \times 10^{-8}$ and $2.1 \times 10^{-9}$ cm$^3$ molec$^{-1}$ s$^{-1}$, respectively. The saturation transfer kinetics is multi-exponential and depends on which pair of rotational states is saturated and probed. Description: Author Institution: Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973-5000 URI: http://hdl.handle.net/1811/30615 Other Identifiers: 2005-TI-08