Syntax error in executable pbs script

Question

I have a pbs script that I am turning into an executable file then trying to run it, however, I am getting a syntax error. The syntax error is listened below:

./run_correlation_study.pbs: line 4: syntax error near unexpected token `then'
./run_correlation_study.pbs: line 4: `      then'

Line 4 is the first line that says "then" under "if[i==0]". I have another pbs script called correlation_study.pbs that is executed in this script along with 3 command line parameters that are incremented by the for loops. I can't quite spot my syntax error though as my script looks similar to all the examples that I have looked at but something is obviously wrong. Below is my script:

for((ARC_LENGTH = 1; ARC_LENGTH < 4; ARC_LENGTH++)); do
    for((i = 0; i < 4; i++)); do
       if[i==0]
         then
         qsub -v ARC_LENGTH_ARG=$ARC_LENGTH,NEUTRINO_BOUNDS=$i correlation_study.pbs
       elif[i==1]
       then 
       qsub -v ARC_LENGTH_ARG=$ARC_LENGTH,NEUTRINO_BOUNDS=$i correlation_study.pbs
       elif[i==2]
       then 
       qsub -v ARC_LENGTH_ARG=$ARC_LENGTH,NEUTRINO_BOUNDS=$i correlation_study.pbs
       elif[i==3]
       then 
       qsub -v ARC_LENGTH_ARG=$ARC_LENGTH,NEUTRINO_BOUNDS=$i correlation_study.pbs
       fi
    done
done