(1)

Sorting out the second integration variable

(2)

Then using the integration template the second integral becomes

   (3)

Putting the exponential with the similar term in the integral over r1 yields

          (4)

The next step for the r1 integration is to combine the powers of r1

                    (5)

and to simplify the factor

                      (6)

and to finally evaluate the last integral

             (7)