Raman Spectral Studies of HTO in H2O

Abstract

Argon‐ion laser Raman spectra have been recorded photoelectrically from a 10 volume % solution of T2O in H2O at temperatures from 26 to 94°C and from a 3.6M ternary solution of NaClO4 in 5 volume % T2O in H2O at 25°C. Laser‐Raman spectra were also obtained from a 10 volume % solution of H2O in D2O at temperatures from ·23 to 96°C. At 26°C, a Raman intensity maximum was observed in the OT stretching region from HTO near Δ ν̄=2130 ± 5 cm −1 , and a shoulder was apparent near Δ ν̄=2225 − 2250 cm −1 . An isosbestic frequency was also indicated for HTO near Δ ν̄=2164 ± 7 cm −1 from 26 to 70°C and for HDO near 3450 cm−1 from ·23 to 63°C. The shapes of the OT and OH stretching contours from HTO and HDO were approximated by two broad Gaussian components using an analog computer, and the resulting plots of log 10 (I NHB / I HB ) vs 1/T , where I NHB refers to the high‐frequency nonhydrogen‐bonded Gaussian component intensity (the shoulder), and I HB refers to the low‐frequency hydrogen‐bonded intensity (the peak), were characterized by values of about 2.5±0.2 kcal/mole OTO and 2.2±0.3 kcal/mole OHO in resonable agreement with a previous two‐Gaussian value of 2.5±0.6 kcal/mole ODO. Two pronounced intensity maxima were also observed in the OT stretching region from the ternary NaClO4 solution near Δ ν̄=2150 ± 5 cm −1 and Δ ν̄=2225 ± 5 cm −1 in general support of the two‐Gaussian analysis of the binary solution stretching contours. The ΔH o values corresponding to the disruption of O – T ··· O , O – D ··· O , and O – H ··· O bonds agree despite the facts that the three contour shapes are different and that the nonhydrogen‐bonded OT stretching component is, relative to the hydrogen‐bonded component, roughly 2 times more intense than the corresponding OD and OH components. The value of ·2.5 kcal/mole hydrogen bond was also found to agree with numerous other experimental ΔH o values, as well as with a recent value from molecular dynamics calculations.