Depletion spectra of the v(1), v(3), and 2v(4) vibrational bands (v = 3000-3500 cm(-1)) of ammonia molecules embedded in He droplets have been studied. The effective rotational constants of ammonia in helium B-He and C-He are found to be about 5% smaller than those of free NH3. The magnitude of the inversion splitting is very close (within 6%) to that in the free molecule. Relaxation times of different rotational levels in the studied vibrationally excited states are estimated to be in the range of 1 x 10(-12)-5 x 10(-11) s and are found to have strong dependence on the rotational quantum numbers. (c) 2005 Elsevier B.V. All rights reserved.