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 acid s 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 th e isolated molecules from seeded beam expansions are interpreted in terms o f the lower temperatures and the suppression of certain conformers in the l iquid helium environment. (C) 1999 American Institute of Physics. [S0021-96 06(99)01302-1].