1. Project the raster using Arc

Project GRID C:\Workspace\temp\mollweide\f2 C:\Workspace\temp\mollweide\f2_mol mollweide.txt BILINEAR

Where mollweide.txt contains...

INPUT
PROJECTION GEOGRAPHIC
UNITS DD
DATUM WGS84
PARAMETERS
OUTPUT
PROJECTION MOLLWEIDE
UNITS METERS
DATUM WGS84
PARAMETERS
00 00 00
END

2. Project the raster using ArcGIS; specify the cell size to match the output from step 1. This grid will be used for the mask since arcgis retains the outer cells as true nulls.

ProjectRaster C:\Workspace\temp\mollweide\f2 C:\Workspace\temp\mollweide\f2_ag_CS C:\Workspace\temp\mollweide\mollweide.prj NEAREST 19675.8392897685

Where mollweide.prj contains ....

PROJCS["World_Mollweide",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Mollweide"],PARAMETER["False_Easting",0],PARAMETER["False_Northing",0],PARAMETER["Central_Meridian",0],UNIT["Meter",1]]

3. Create a mask in ArcInfo GRID

 mask = con( f2_ag_CS >= 0, 1)

4. Also in ArcInfo GRID, Apply the mask to the output from step 1

 f2_molclip = con( mask == 1, f2_mol )