Pure second order Stark effect:
      E.level = E.o + ( A.g + B.g M^2 ) mu.g^2 E^2
 Mixed order:
      E.level = (E1+E2)/2  +- [ (DE/2)^2 + mu.g^2 E^2 |xi|^2 M^2 ]^(1/2)

              = E1-DE/2+[...]^(1/2) and
                E2+DE/2-[...]^(1/2) for E1>E2, DE=E1-E2

 * E1,E2,DE should in general be inclusive of second order Stark contributions
 * Asterisk denotes levels implicated in near degeneracy for which
   A and B are evaluated without the connecting (|Phi.Zg|) term
 * Sum field contributions for more than one dipole component
 * Dipoles in D, energies in MHz, field in V/cm
 * In the .INT file set mu.g to 1 (only one at a time) and STRFLG=1

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  H2O...HF                                                       
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           A.g           B.g       level                         g

 DE=  123.5200 |xi|= 2.517046E-01  1 1 0      <-> 1 1 1          1

   -5.865001E-06     5.865001E-06  0 0 0                         1    1
 DE=  370.5600 |xi|= 8.390188E-02  2 1 1      <-> 2 1 2          1
 DE=     .0291 |xi|= 1.678036E-01  2 2 0      <-> 2 2 1          1

 * -1.752535E-06     4.381338E-07  1 1 0                         1    1
 * -1.767634E-06     4.419086E-07  1 1 1                         1    1
    3.518901E-06    -5.278476E-06  1 0 1                         1    1
 DE=     .0000 |xi|= 1.258529E-01  3 3 0      <-> 3 3 1          1
 DE=     .1457 |xi|= 8.390214E-02  3 2 1      <-> 3 2 2          1

 * -8.388762E-07     9.320847E-08  2 2 0                         1    1
 * -8.388785E-07     9.320872E-08  2 2 1                         1    1
 *  4.171609E-07    -2.897589E-07  2 1 1                         1    1
 *  4.207541E-07    -2.922552E-07  2 1 2                         1    1
    8.377670E-07    -4.189325E-07  2 0 2                         1    1
 DE=     .0000 |xi|= 7.551164E-02  4 3 1      <-> 4 3 2          1
 DE=     .4370 |xi|= 5.034110E-02  4 2 2      <-> 4 2 3          1
 DE=     .0000 |xi|= 1.006822E-01  4 4 1      <-> 4 4 0          1

 * -4.900798E-07     3.062999E-08  3 3 0                         1    1
 * -4.900798E-07     3.062999E-08  3 3 1                         1    1
 * -9.479126E-11    -4.077278E-08  3 2 1                         1    1
    3.909241E-07    -9.775453E-08  3 0 3                         1    1
    2.945121E-07    -2.458507E-06  3 1 3                         1    1
    2.919971E-07     2.291462E-06  3 1 2                         1    1
 * -9.677752E-11    -4.077277E-08  3 2 2                         1    1
 DE=     .0001 |xi|= 5.034112E-02  5 3 2      <-> 5 3 3          1
 DE=     .0000 |xi|= 8.390187E-02  5 5 0      <-> 5 5 1          1
 DE=    1.0198 |xi|= 3.356075E-02  5 2 3      <-> 5 2 4          1
 DE=     .0000 |xi|= 6.712149E-02  5 4 1      <-> 5 4 2          1

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