OH bonds in electric fields: electron densities and vibrational frequency shifts

✍ Scribed by Kersti Hermansson

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 605 KB
• Volume: 233
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(94)01458-8

✦ Synopsis

The changes in the electron density distribution caused by varying the O-H bond length for HDO and OH-in uniform electric fields are investigated and related to the frequency shifts for the uncoupled O-H stretching vibration. Numerical integration of difference density maps, Ap= p( roH + ArOH) -p( rOH), reproduces the electronic contribution to apii""I/ at-,, , if the integration is carried out to a distance of = 3.5 A from the 0 atom. The frequency shift A v is proportional to -E,, x [d/Ltp"="' (IoH) /dr&-&% VP iyduced( E,, , rOH) /&-OH] and electron density maps corresponding to the electronic parts of these terms are presented. Experimentally it has been found that the OH -ion shows a frequency upshift when bound in a moderately strong field, while water molecules show a downshift. The electron density maps show why dpr"'-"'( roH) /drOH is positive for HDO and negative for OH -, resulting in a downshift for bound water an an upshift for bound OH-. For positive fields, a~~;dUCedl aroH is positive for both HDO and OH -and gives a downshift contribution.