What you want is a particle beam, specifically a hydrogen beam - also called proton beam.
More details on weaponized space particle beams here and here (from the always interesting ToughSF blog), but here are the elements that are important for the question:
Neutral particle beams accelerate ions and electrons before recombining them into neutral atoms. This last step is important because charged particle beams (like electron beams), while easier to produce, repel themselves and disperse rapidly, considerably decreasing their range. In addition, they are easier to protect from with magnetic fields, and create dangerous charges on the emitter. So neutral particle beams it is.
The problem is that particles are stopped by matter, and you want to fire through the atmosphere. Here is where things start being counter-intuitive. You would expect heavier particles to travel further before being stopped, but in fact the opposite is true: the lighter the atom nucleus, the further it will go for the same energy. And the lightest nucleus is a simple proton, from hydrogen atoms.
Intuitively, you would also expect how far particles go to continuously decrease the further you go, with more particles being stopped in the first 10cm than in the 10cm one meter past. however, most protons actually cross some distance unimpeded before being stopped en masse, something that is called a Bragg peak. Which is good for you, as you can fire with just the right energy so the Bragg peak is right in the middle of the squishy humans instead of in the atmosphere, building wall or tank armor.
With powerful enough emitters, you can even hit deep underground bunkers, though this require some hefty beams. At this point, you may even switch to antihydrogen beams to pack an extra punch - antiprotons beams seem to mostly work the same way than proton beams in that regard.
Hydrogen is better than neutrons for a few reasons: neutrons don't have a Bragg peak, so they aren't that good at penetrating hits. In addition, collimated neutron beams are very difficult to produce, and neutron activation will cause more material to become radioactive, which you do not want here.
What about the electron, one may ask. It is mostly negligible (beyond neutralizing the beam), as its mass (and thus the damage it will cause) is about a thousand times less than the mass of the proton.
Do note that while there have been some tests made for hydrogen beams as a space-to-space weapon, you would need much more energetic beams than could be put in orbit with today's tech for an orbit-to-surface weapon.