The journey to accurately determine the geometric structure of a water molecule is a fascinating chapter in the history quantum mechanics. Linus Pauling, in 1931, first estimated the angle to be 90°, utilizing the then-novel approximations in quantum mechanics. This initial approximation was further investigated in E. K. Plyler's paper, Phys. Rev. 39, 77 (1932), where the angle was calculated based on the infrared absorption frequencies of water. The results came remarkably close but were not precise, resulting in an angle of 115°. A significant development occurred in 1945, with the publication of the book G. Herzberg, Molecular Spectra and Molecular Structure Vol. II, which for years was considered the authoritative source for the water molecule's angle. The data derived from a series of experiments conducted by R. Mecke and his team from 1933 to 1942, mainly reported in German. From their infrared spectroscopy studies, the angle was deduced to be 104.45°. The scientific expedition to unravel the geometric structure of a water molecule serves as a reminder of the persistent pursuit of truth that marks every scientist's quest.

Millennium Prize Problems progress after 21 years ▓▓░░░░░░░░░░░░░ 14% (1/7 solved - Poincaré Conjecture)