Formation of Semi-Covalent Bond in [(N2O)nH2O]+ (n = 2-7) Cluster Ions Studied by IR Spectroscopy

IR photodissociation (IRPD) spectra of [(N2O)nH2O]+ with n = 2－7 are measured in the 1100－3800 cm-1 region. In parallel, the geometry optimization and the vibrational analysis are carried out at the B3LYP/6-311++G(d,p) level of theory. In the OH stretching (2400－3800 cm-1) region, the IRPD spectrum of the [(N2O)2H2O]+ ion shows a sharp band at 3452 cm-1 and a broad one at around 2700 cm-1, which are assignable to the stretching vibrations of the free and hydrogen-bonded OH groups, respectively. The IRPD spectra of the [(N2O)nH2O]+ (n = 3－7) ions show no band of the free OH stretching vibration, indicating that both of the OH groups are hydrogen-bonded to solvent N2O molecules. The IRPD spectra of the n = 2－7 ions also show the ν1 and ν3 vibrations of the N2O components at around 1250 and 2200 cm-1, respectively. Comparison of the IRPD spectra with the calculated IR spectra suggests that the [(N2O)nH2O]+ cluster ions have an (N2O･H2O)+ ion core, in which the positive charge is delocalized over the H2O and N2O components, and that an intermolecular semi-covalent bond is formed between the oxygen atoms of H2O and N2O through the charge resonance interaction.This is a preprint of an article published by American Chemical Society in Journal of Physical Chemistry A, 2010, available online: http://pubs.acs.org/doi/abs/10.1021/jp100336h.This work is supported by Grant-in-Aids (Grant Nos. 18205003 and 21350016) for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT)