CCL:G: how to freeze in gaussian

["kiran k" <kd2f[-]mtmail.mtsu.edu>]

 Sent to CCL by: "kiran  k" [kd2f..mtmail.mtsu.edu]
 Dear CCLusers,
 Could anyone suggest how to find interaction energy between formaldehyde and
 fluoride ion in gaussian using z-matrix, by keeping the distance constant.
 After the calculation, the distance changed. Here is my example input look
 like
  ----------------------------------------------------------------------
 #P B3LYP/6-31+G* opt Test
 Geometry Optimization
 -1 1
 C
 O  1  r2
 F  1  r3  2  a3
 H  1  r4  2  a4  3  d4
 H  1  r5  2  a5  3  d5
 Variables:
 r2= 1.2246
 a3=  90.00
 r4= 1.1017
 a4= 122.24
 d4= 354.18
 r5= 1.1017
 a5= 122.24
 d5= 174.18
 constant:
 r3= 2.5000
 Thank you in advance