IRON PLAYS AN IMPORTANT ROLE IN ASTROPHYSICS. HAVING THE ONE OF THE MOST STABLE BINDING ENERGIES OF ANY ELEMENT IT RANKS 9TH IN OVERALL COSMIC ABUNDANCE WITH FEH 3 10-5. IT IS SUFFICIENTLY PREVALENT TO BE ROUTINELY USED AS A MEASURE OF METALLICITY IN STARS FROM ITS OPTICAL TRANSITIONS. IN THE DIFFUSE INTERSTELLAR MEDIUM IRON APPEARS TO BE DEPLETED IN THE GAS-PHASE BY ONE TO TWO ORDERS OF MAGNITUDE BASED ON ULTRAVIOLET ABSORPTION LINES SUGGESTING THAT THE ELEMENT IS INCORPORATED INTO DUST GRAINS. THE COMMON OCCURRENCE OF IRON IN METEORITES AND PRESOLAR GRAINS BOLSTERS THIS CONCEPT. ON THE OTHER HAND TYPE IA SUPERNOVAE AN MAJOR SOURCE OF IRON SHOW NO EVIDENCE OF DUST GRAINS IN THEIR EJECTA. THIS RESULT SUGGESTS THAT A LARGE PORTION OF IRON REMAINS IN THE GAS PHASE. SOME FRACTION OF THIS GAS-PHASE IRON COULD BE IN MOLECULAR FORM. FEH AND ITS CORRESPONDING ION FEH+ ARE EXCELLENT MOLECULAR CANDIDATES GIVEN THE ABUNDANCE OF INTERSTELLAR HYDROGEN. FEH ITSELF HAS ALSO BEEN OBSERVED IN THE ATMOSPHERES OF M-TYPE STARS AND L-TYPE BROWN DWARFS VIA ELECTRONIC TRANSITIONS IN THE NEAR-INFRARED. HOWEVER PROBABLY THE BEST TECHNIQUE FOR STUDYING FEH AND FEH+ IN THE GENERAL INTERSTELLAR MEDIUM IS VIA THE PURE ROTATIONAL TRANSITIONS OF THESE SPECIES WHICH BECAUSE THEY ARE HYDRIDES ONLY OCCUR AT SUBMM/THZ/INFRARED WAVELENGTHS AND ARE OFTEN INACCESSIBLE BY GROUND-BASED TELESCOPES. THEREFORE FEH AND FEH+ ARE EXTREMELY GOOD TARGETS FOR SUBMM/ THZ NASA MISSIONS. THE PURPOSE OF THIS PROPOSAL IS TO ASSEMBLE A COMPLETE DATABASE OF DIRECTLY MEASURED HIGHLY ACCURATE (1 PART IN 107) ROTATIONAL REST FREQUENCIES FOR FEH ITS DEUTERIUM ISOTOPOLOGUE FED AND ITS IONIC FORMS FEH+ AND FED+ IN THE FREQUENCY RANGE 0.5 2 THZ. SUCH A DATA SET DOES NOT EXIST FOR EITHER SPECIES IN PART BECAUSE SPECTROSCOPY OF THESE MOLECULES IS NOT TRIVIAL. FEH HAS A HIGHLY PERTURBED 4I GROUND ELECTRONIC STATE WHICH PRECLUDES PREDICTION OF THE THZ REST FREQUENCIES FROM KNOWN INFRARED CONSTANTS. THERE IS NO SPECTROSCOPIC DATA OF ANY SORT FOR FEH+ AND EVEN ITS GROUND ELECTRONIC STATE IS UNCERTAIN ALTHOUGH THEORY SUGGESTS IT IS 5I. THIS PROJECT IS WELL-MATCHED TO THE PI S EXTENSIVE EXPERIENCE IN MEASURING AND ANALYZING THE SPECTRA OF IRON-BEARING MOLECULES WITH EXOTIC GROUND STATES INCLUDING THOSE WITH PERTURBATIONS (E.G. FEC (X3I) FEO (X5I) FEN (X2I) FECN (X4I) FENC (X4I) FEO+ (X6S+)). FURTHERMORE THE PI AND HER GROUP ALREADY HAVE PRELIMINARY MEASUREMENTS OF A FEW SUB-MM TRANSITIONS OF FEH AND FED AND THUS THE SUCCESS OF FUTURE WORK IS HIGHLY PROBABLE. THE TECHNIQUE TO BE EMPLOYED FOR THE MEASUREMENTS IS SUBMM/ THZ DIRECT ABSORPTION SPECTROSCOPY. THREE WORKING PROVEN SPECTROMETERS ARE AVAILABLE FOR THIS WORK AND THE PI HAS ALREADY DEVELOPED THE UNUSUAL GAS-PHASE SYNTHETIC TECHNIQUES NECESSARY TO CREATE THESE UNSTABLE SPECIES AND THE SPECTROSCOPIC EXPERTISE TO ANALYZE THEIR OPEN-SHELL ELECTRONIC STATES. IN ADDITION HIGHLY ACCURATE QUANTUM CHEMICAL CALCULATIONS WILL BE PERFORMED FOR FEH AND FEH+ TO PROVIDE ADDITIONAL MOLECULAR PROPERTIES (DIPOLE MOMENTS LINE STRENGTHS) AS WELL AS ASSIST IN PREDICTING THE GROUND ELECTRONIC STATE OF THE ION. OBSERVATIONS CONDUCTED IN THE PAST WITH HERSCHEL SPACE OBSERVATORY AND CURRENTLY SOFIA HAVE CLEARLY DEMONSTRATED THAT SIMPLE HYDRIDE MOLECULES SUCH AS NH CH+ HF SH+ HCL+ AND OH+ ARE COMMON CONSTITUENTS OF MANY REGIONS OF THE INTERSTELLAR MEDIUM EVEN THOSE WITH A RARE ELEMENT SUCH AS F OR CL. MOREOVER OTHER IRON-CONTAINING MOLECULES HAVE BEEN OBSERVED IN CIRCUMSTELLAR GAS (FECN IN THE OUTER ENVELOPE OF THE LATE-TYPE CARBON STAR IRC+10216) AND POSSIBLY IN DENSE MOLECULAR CLOUDS (FEO IN SGR B2(M)). IT WOULD SEEM FEASIBLE THAT OTHER FE-BEARING SPECIES WOULD BE PRESENT IN INTERSTELLAR GAS. HYDRIDES HAVE LONG BEEN CONSIDERED THE BUILDING BLOCKS OF ASTROCHEMISTRY