Ny research benefit from getting an intact weapon

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If I managed to capture an alien with Arc-Thrower I think I get its weapon intact.
If I don't have it researched yet

Will I be able to use it? (I assume answer is no but not sure)
Will It give me any research benefit? (It is logical to think it will be easier to research on an intact plasma rifle over weapon fragments)

You cannot use any weapon until you research it
Intact weapon is prerequisite for research
If you captured more weapons of a kind before researching it, you'll still be able to use all of them once you researched it.
In case of alien grenade, there is a Foundry Project, which gives you infinite supply. You only need one alien grenade for that.
There is absolute no point in capturing more than 6 of particular kind. In fact, for most it's even less (heavy can't use pistol nor rifle, sniper can't use rifle)
Capturing weapon means no weapon fragments, which are necessary for most research and foundry projects.
On rare occasions Council Request for weapons will appear. You have absolutely no control over when and which weapons.