def parseApproxArcCoordsFile(fileName):
    """Returns a dictionary indexed by x coord of line wavelengths in Angstroms.
    
    """
    inFile = open(fileName, 'r')
    lines = inFile.readlines()
    inFile.close()
    coordsDict = {}
    for line in lines:
        if len(line) > 3 and line[0] != '#':
            bits = line.split()
            coordsDict[int(bits[1])] = float(bits[0])
    return coordsDict
