H _ { 2 } O ^ { + } has been observed in its ortho - and para - states toward the massive star forming core Sgr~B2 ( M ) , located close to the Galactic center .
The observations show absorption in all spiral arm clouds between the Sun and Sgr B2 .
The average o/p ratio of H _ { 2 } O ^ { + } in most velocity intervals is 4.8 , which corresponds to a nuclear spin temperature of 21 K. The relationship of this spin temperature to the formation temperature and current physical temperature of the gas hosting H _ { 2 } O ^ { + } is discussed , but no firm conclusion is reached .
In the velocity interval 0-60 km s ^ { -1 } , an ortho / para ratio of below unity is found , but if this is due to an artifact of contamination by other species or real is not clear .