A sesquioxide is an oxide containing three atoms of oxygen with two atoms (or radicals) of another element. For example, aluminium oxide (Al2O3) is a sesquioxide.
Many sesquioxides contain the metal in the +3 oxidation state and the oxide ion, e.g., Al2O3, La2O3. The alkali metal sesquioxides are exceptions and contain both peroxide, and superoxide, ions, e.g., Rb2O3 is formulated [(Rb+
2]. Sesquioxides of iron and aluminium are found in soil.
Sesquioxidizing, meaning the creation of a sesquioxide, is the highest scoring word that would fit on a Scrabble board, though it does not actually appear in any official Scrabble dictionary. Though the Oxford English Dictionary already listed the noun and the past participle adjective -- sesquioxidation and sesquioxidized, respectively -- the verb, sesquioxidize, and its conjugated forms, have been absent from the dictionaries used as sources for the official Scrabble word lists. An early appearance of the noted present participle had occurred in the 1860 publication of the State of New York's Legislative Assembly's Transactions of the State Medical Society, yet the word's first appearance in a dictionary was in the 1976 edition of Josepha Heifetz Byrne's Mrs. Byrne's Dictionary of Unusual, Obscure, and Preposterous Words (ISBN 0806504986), One could theoretically score 2044 points in a single move, when otherwise only words from the official Scrabble word list are used.