Those special characters are part of the part of the extension to the ASCII and are meant to supplement other characters (the previous one to be precise) such that combined they form letters like á, â, ä, etc. As far as I'm aware you won't be able to write them by themselves with a single keystroke, but you can type them once entering the state of "waiting for the following" character, and then press the right arrow key which would drop them into place.
If you need to use them as part of some script then you'd have to resort to a key combination using the exact code representation.