We extend the theory of combinatorial link Floer homology to a class of oriented
spatial graphs called transverse spatial graphs. To do this, we define the notion of a
grid diagram representing a transverse spatial graph, which we call a graph grid
diagram. We prove that two graph grid diagrams representing the same transverse
spatial graph are related by a sequence of graph grid moves, generalizing the work of
Cromwell for links. For a graph grid diagram representing a transverse spatial graph
, we
define a relatively bigraded chain complex (which is a module over a multivariable
polynomial ring) and show that its homology is preserved under the graph grid
moves; hence it is an invariant of the transverse spatial graph. In fact, we define
both a minus and hat version. Taking the graded Euler characteristic of
the homology of the hat version gives an Alexander type polynomial for
the transverse spatial graph. Specifically, for each transverse spatial graph
, we define a balanced
sutured manifold
.
We show that the graded Euler characteristic is the same as the torsion of
defined by S Friedl, A Juhász, and J Rasmussen.