What is the product of H2 and O2 burning ? Are any other gasses produced ?

no, what your describing is what nasa uses at rocket propellent....

liquid hydrogen and liquid oxygen,

and they both burn 100% clean, i thnk together they produce water.....

hydrogen (H2) burned with pure oxygen (O2), the only by products are heat and water. When burned with air, which is about 68% nitrogen, some oxides of nitrogen (or NOx) are formed

In fuel cells, electrolysis is reversed by combining hydrogen and oxygen through an electrochemical process, which produces electricity, heat, and water

ps. if by chance you have pure h2, dont smoke or have sparks.h2 is 50 times more explosive than gas. and a much greater chance of flash and reflash. Eventhough Hydrogen is the simplest and most common element in the universe. It has the highest energy content per unit of weight.

taken from scent3.com, i love to research. RNX57%

water