Hyperfine structure of the MnH X 7Σ+ state: A large gas-to-matrix shift in the Fermi contact interaction

Abstract

Sub-Doppler spectra of the A 7Π–X 7Σ+ (0,0) band of gas phase MnH near 5680 Å were recorded by intermodulated fluorescence spectroscopy. The spectra reveal hyperfine splittings arising from both the 55Mn and 1H nuclear spins. Internal hyperfine perturbations have been observed between the different spin components of the ground state at low N″. From a preliminary analysis of several rotational lines originating from the isolated and unperturbed F1(J″=3) spin component of the X 7Σ+(N″=0) level, the 55Mn Fermi contact interaction in the ground state has been measured as bF=Aiso =276(1) MHz. This value is 11% smaller than the value obtained by Weltner et al. from an electron-nuclear double resonance (ENDOR) study of MnH in an argon matrix at 4 K. This unprecedented gas-to-matrix shift in the Fermi contact parameter is discussed.