You may first expand your expression. Then you may collect all terms containing x/y and all terms not containing x/y.

Now, in your example, every term contains x because of the prefactor: ` E^(I (t (v - 2 w) + x))`

. I therefore delete the `x`

in the prefactor to get a more telling example:

```
f(x_, y_, z_, t_, w_, v_) :=
E^(I (t (v - 2 w))) (2 E^(I (3 t v + y)) + 16 E^(I (2 t w + y)) +
2 E^(2 I t w) t^4 + 3 E^(I t (v + w)) t^4 + 2 E^(4 I t w) t^5 -
2 E^(I t (v + 3 w)) t^5 + E^(I (2 t v + y)) t^6 +
8 E^(I (3 t v + 2 t w + y)) t^6);
```

Now we assemble the terms with and without x/y:

```
fwith = Select(Expand@f(x, y, z, t, w, v), FreeQ(#, x | y) &) // Simplify
fwithout = Select(Expand@f(x, y, z, t, w, v), ! FreeQ(#, x | y) &) // Simplify
```

And finally, if needed, you may redefine the original function:

```
fnew(x_, y_, z_, t_, w_, v_) := fwith + fwithout
fnew(x, y, z, t, w, v)
```