*cd lsthleps
**     common / leps / de(3), beta(3), r0(3), delta(3), vbase
*cd lsthpotc
**     common / potcom / c6,c8, rkw(87), ekw(87), wkw(87)
*dk lsth
      subroutine lsth(potntl,dist)
c
      implicit real*8 (a-h,o-z)
c  returns the h3 lsth surface in au relative to bottom of asymptotic well.
*ca lsthpotc,lsthleps
      common / leps / de(3), beta(3), r0(3), delta(3), vbase
      common / potcom / c6,c8, rkw(87), ekw(87), wkw(87)
      dimension dist(3)
      external lsthdata
      data ncall / 0 /
      data conv1, conv2, conv3 / .529177249d-8, 27.2113961d0,
     >     1.60217733d-12 /
      if ( ncall .gt. 0 ) go to 1
      do 100 i = 1, 87
      rkw(i) = rkw(i)/conv1
      ekw(i) = ekw(i)/(conv2*conv3)
      wkw(i) = wkw(i)/(conv2*conv3)*conv1*conv1
  100 continue
      c6 = c6/(conv2*conv3*conv1**6)
      c8 = c8/(conv2*conv3*conv1**8)
      ncall = 1
    1 continue
c  unblock the next two cards to clip the potential.
      potntl=10.0d0
      if(min(dist(1),dist(2),dist(3)).lt.0.001d0) return
      call lsthpot ( dist, v )
      potntl = v
c  convert  to au from bottom of h2 well.
      potntl = (potntl+0.174475d0)
      return
      end