High sensitivity and precision spectroscopy in the far infrared AIP Conf.The laser excitation spectrum of tungsten methylidyne, WCH, has been recorded in the 12 000-15 400 cm Ϫ1 region. A total of 14 vibronic bands of WCH and 16 bands of WCD have been observed in this region. Rotational analysis shows that the ground state is X3/2( 2 ⌬), with the substitution structure r 0 ͑WwC͒ϭ1.7366 5 Å and r 0 ͑C-H͒ϭ1.076 5 Å. The excited vibronic levels have been assigned, on the basis of their WCH/WCD isotope shifts and their wavelength resolved fluorescence patterns, to three electronic states, Ã3/2( 2 ⌬), B1/2( 2 ⌸), and C 5/2( 2 ⌽), at 12 090, 13 392, and 14 110 cm Ϫ1 , respectively. The wavelength resolved fluorescence spectra have also established the low-lying vibrational levels of the ground state. The ground state bending fundamental lies at 660 cm Ϫ1 , while the W-C stretching frequency is 1006 cm Ϫ1 ; the corresponding frequencies in WCD are 501 cm Ϫ1 and 953 cm Ϫ1 , respectively. No evidence for the C-H stretching frequency has been found. Emission has also been observed to a low-lying electronic state, 813 cm Ϫ1 above the X3/2 state. The pattern of rotationally resolved emission to this state clearly indicates that it is a 4 ⌺ 1/2 state. Its bending frequency is 612 cm Ϫ1 , and its W-C stretching frequency is 971 cm Ϫ1 , indicating a slightly longer bond length than in the X3/2 state. High resolution cw laser spectra of the ͑0,0͒ bands of the two lowest excited electronic states ͓Ã3/2( 2 ⌬) and B1/2( 2 ⌸)͔ reveal a small splitting of the four principal tungsten isotopes ͑ 182 W, 183 W, 184 W, and 186 W͒ which serves to confirm the presence of tungsten in the carrier. Hyperfine splitting associated with the 183 W nucleus (Iϭ1/2) has been observed for the ͑0,0͒ band of the Ã3/2ϪX3/2 system, allowing the electron configuration of the ground state to be elucidated.