Identity of the Zwischenspiel

The work consists of six movements with a "Zwischenspiel" (intermezzo) between the fifth and sixth movements.
This Zwischenspiel (of completely desolate and serene character, forming a large contrast with the previous movements of the piece) appears to be at the Golden Section point in the composition.

The Zwischenspiel consists of three sections. The two outer (first and third) sections are built up by chromatic clusters and function as independent sound. The middle section consist of a repetition of two diatonic clusters.
Cluster 1 is built up by two bunches, each consisting of three minor seconds. The interval between those two bunches is a major third (B-flat, D). The interval seperating the two bunches of minor seconds in Cluster 2 is a major second (B, C-sharp).

The first cluster is written in a way that fits the string-instruments; all four play an individual perfect fifth. Rihm uses this way of writing chords or clusters more often in this piece. For instance:

The middle section becomes independent sound as soon as the composer prescribes: "Asynchron werden" (become non-synchronized).
If looked at the independant voices one could say every instrument repeats playing an interval of a minor second. The first note could be regarded as an appogiatura (I will use this term since traditionally it is mainly a melodic non-harmonic ornament; I could have used such terms seufzer, anticipation, suspension, auxiliary- or passing note) leaning on the second one, which is the solution.
Anticipation, or tension, and resolution, or at least the expectation of resolution brought about, are important characteristics in the rest of the piece. The near absence of tension is what makes the Zwischenspiel so suddenly different from the rest.