HCl_data_JGR_Olsen_2024a.hdf5 is an hdf5 file that contains the retrieved HCl and H2O
vertical profiles generated for, and supporting Olsen et al 2024a. 
It can be read using standard hdf45 tools.

For example, in Pythin using h5
with h5py.File('HCl_data_JGR_Olsen_2024a_test.hdf5','r') as fin:
   for key in fin.keys():
      ....

The keys are the occultation names for analyzed ACS MIR observations.
For each of these, the following sub keys are stored:
Ls                   (solar longitude)
LT                   (local time)
Lat                  (latitude)
Lon                  (longitude)
HCl_vmr_ppbv         (VMR of HCl in ppbv)
HCl_vmr_uncertainty  (uncertainty in the HCl VMR in ppbv)
HCl_vmr_Z            (tangent heights for HCl_vmr_ppbv and HCl_vmr_uncertainty)
H2O_vmr_ppbv         (VMR of H2O in ppbv)
H2O_vmr_uncertainty  (uncertainty in the H2O VMR in ppbv)
H2O_vmr_Z            (tangent heights for H2O_vmr_ppbv and HCl_vmr_uncertainty)

Also included, where available, are temperature vertical profiles from ACS NIR
These are from Fedorova, A. A., et al. (2023). A two-Martian year survey of the water vapor
saturation state on Mars based on ACS NIR/TGO occultations. J. Geophys. Res., 128 (1), e2022JE007348. 
doi: 10.1029/2022JE007348
NIR_T                (temperature in K)
NIR_T_err            (uncertainty in temperature)
NIR_Z                (tangent heights in km for NIR T and P)
NIR_P                (pressure in atm)
NIR_P_err            (uncertainty in pressure)

Note that both H2O and HCl may not be retreived for every occultation

to obtain a list of occultations in this file and the Lss/lats covered, something like this works:

with h5py.File('HCl_data_JGR_Olsen_2024a_test.hdf5','r') as fin:
   occnames = list(fin.keys())
   Lslist = [float(fin[key]['Ls'][...]) for key in fin.keys()]
   latlist = [float(fin[key]['Lat'][...]) for key in fin.keys()]
Lsdict = dict(zip(occnames,Lslist))
latdict = dict(zip(occnames,latlist))