Doppler-free saturation spectroscopy of pOlyatomic molecules:
نویسندگان
چکیده
Doppler-free spectra of two vibronic bands in the Ä (IB 3u ).-X (lAg) transition of the photochemically instable s-tetrazine (H2C2N4 ) are presented. For the first time saturation spectroscopy is successfully applied to a large polyatomic molecule. Photochemical decomposition of s-tetrazine molecules takes place after excitation and prevents the molecule from returning to the ground state by radiation and nonradiative processes. This represents a particular type of hole burning in the ground state velocity distribution. The elimination of the inhomogeneous Doppler broadening enables us to determine collisionless homogeneous linewidths. For the 0-0 band a value of r = 190 MHz is found whereas the l6a: band at higher excess energy (vi6a = 256 cm I) shows a sharper linewidth of r = 140 MHz. No rotational dependence of the linewidth is found in the 0-0 band up to J levels higher than 70. It is argued that internal conversion to the X (lAg) state is the process responsible for the observed linewidths and that dissociation takes place on the electronic ground state potential surface.
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