Abstract

To address the vibrational population changes of deoxy-Hemoglobin following photoexcitation(1,2) we have measured the anti-Stokes/Stokes ratio of ν₇, the strongest mode in the low frequency region of the spectrum and find an area ratio of 6.7% to 10.2%. Several observations suggest that this mode is not vibrationally hot on a 30ps timescale. 1) A two color pump/probe protocol using a strong 532nm pump pulse temporally and spatially overlapped with the 436 nm probe pulse resulted in no change in the relative intensities. 2) Experiments using 10ns pulses at the same wavelength yield an anti-Stokes/ Stokes ratio of 8.6% for the 674 cm⁻¹ mode. 3) The anti-Stokes/Stokes ratio is consistent with the value expected at 300K (The Boltzmann ratio of ν₇ corrected with a Kramers-Kronig transform technique is 8.2%). Figure 1 shows the anti-Stokes and Stokes Raman spectra of deoxy-Hb taken with 30ps pulses of three heme modes, ν₇, ν₁₆, and ν₃₂ at 671, 756, and 790 cm⁻¹ respectively.

© 1990 Optical Society of America