Sub-doppler spectroscopy of the [formula omitted]′ v2 = 2 Rydberg level of ND 3 at vacuum ultraviolet energies

Abstract

A pulsed dye laser amplifier for cw lasers has been constructed. By frequency doubling the output pulses, and using counter-propagated beams with 2 + 1 multiphoton ionisation detection, very high resolution spectroscopic studies of atomic and molecular states lying at vacuum ultraviolet energies have become possible. The effective VUV two-photon bandwidth was determined from a sub-Doppler 6s7s 1S 0−6s 2 1S 0 excitation spectrum of mercury vapour, and found to be 275 MHz (0.009 cm −1) fwhm. The 2 2 0 band in the C ′ 1A′ 1 X 1A 1 Rydberg transition of ND 3 shows very narrow sub-Doppler linewidths, of which the narrowest, with J = K = 0, has a deconvoluted homogeneous width of 350 MHz in our experiment, corresponding to a lifetime of 0.45 ns. The general trend of an increase in linewidth with rotational excitation is consistent with rovibronic coupling to the continuum of the A 1A″ 2 state. In addition, a number of apparently random level shifts and anomalously weakened lines is attributed to a perturbation, most probably by the overlapping and more severely predissociated v 2 = 8 level of the B 1E″ state, acting as an additional doorway to the dissociative à state levels.