High resolution vibronic spectra of the amino acids tryptophan and tyrosine in 0.38 K cold helium droplets

High resolution vibronic absorption spectra are reported for the amino acids tryptophan and tyrosine embedded in large (N similar or equal to 10(3) - 10(4)) helium droplets. The spectra exhibit a large number of sharp (delta nu approximate to 0.5 cm(-1)) 0(0)(0) band origins which are attributed to different conformers. The significant differences to previous spectra of the isolated molecules from seeded beam expansions are interpreted in terms of the lower temperatures and the suppression of certain conformers in the liquid helium environment. (C) 1999 American Institute of Physics. [S0021-9606(99)01302-1].