3 lvl 1 characters vs CR 2 is 200 exp, yeah.
I cant find rules for characters under lvl 1,
There aren't any, as far as I know. However, the encounter calculator on the SRD uses "party level" as a factor, so if you wanted to follow that logic...
The "level" of the party is calculated as 0.25 x the level of each character, so for example, 2 level 1 characters would be a 0.5 level party. For experience point rewards, you'd then just treat the party as though they were made up of "n" characters, where 0.25 x "n" = the "level" of the party. This sounds complicated, but since both the party level and experience point fractions are linear, you can simply divide their experience point rewards by 4 times the effective party level. For example:
A. A party of 8 level 1 fighters kills a CR 2 monster. Each character is slated to get 600 exp (exp for a level 1 character killing a CR 2 Monster), but that's divided by the number of characters in the party (8) for a final total of 600/8=75 EXP per character.
B. The same party does the same thing, but for whatever reason, you decide to calculate EXP rewards based on party level, instead. The party level is 2 (0.25 x 8), so the EXP reward per person is whatever they'd get for individually defeating the monster (600) divided by 4 x the party level (8), or 600/8 = 75 EXP.
C. 3 level 1 factotums defeat a CR 2 encounter, but for whatever reason, they gain EXP as though their party level was 1/3. Each is level 1, so for a CR 2 monster, that's 600 EXP per person; divide that by 4 x the party level and you get
600 / (4/3) = 450 EXP apiece.
This is based off of the encounter calculator linked to on d20srd.org, where small parties are assigned fractional "party levels"; it's not RAW as far as I can tell, but in my opinion it makes some sense.
But all of this is for use at the DM's discretion; as with all EXP rewards, it's just as logical to say "you all get 100 exp" since tailoring rewards is a big part of the DM's job