(Sorry about the delay, waiting on a ruling from the DM on something.)
Targeting an item for damage is done by the sunder mechanic.
Sunder
You can attempt to sunder an item held or worn by your opponent as part of an attack action in place of a melee attack. If you do not have the Improved Sunder feat, or a similar ability, attempting to sunder an item provokes an attack of opportunity from the target of your maneuver.
If your attack is successful, you deal damage to the item normally. Damage that exceeds the object's Hardness is subtracted from its hit points. If an object has equal to or less than half its total hit points remaining, it gains the broken condition (see Conditions). If the damage you deal would reduce the object to less than 0 hit points, you can choose to destroy it. If you do not choose to destroy it, the object is left with only 1 hit point and the broken condition.
If the intent was to just be able to target items(attended) at will by using hit point damage this mechanic would not be needed. The only way I know of that allows an item to be targeted with ranged attacks is the fighter(archer archetype)
Trick Shot (Ex): At 3rd level, an archer can choose one of the following combat maneuvers or actions: disarm, feint, or sunder. He can perform this action with a bow against any target within 30 feet, with a –4 penalty to his CMB. Every four levels beyond 3rd, he may choose an additional trick shot to learn. These maneuvers use up arrows as normal.At 11th level, he may also choose from the following combat maneuvers: bull rush, grapple, trip. A target grappled by an arrow can break free by destroying the archer's arrow (hardness 5, hit points 1, break DC 13) or with an Escape Artist or CMB check (against the archer's CMD –4). This ability replaces armor training 1, 2, 3, and 4.
Disintegrate can attack objects, just like an archer can, but I see nothing that says it gets a rules exception allowing it to target attended items.
Compare to "rusting grasp" which specifies it can be used against attended objects.
Any iron or iron alloy item you touch crumbles into rust. If the item is so large that it cannot fit within a 3-foot radius, a 3-foot-radius volume of the metal is rusted and destroyed. Magic items made of metal are immune to this spell.
You may employ rusting grasp in combat with a successful melee touch attack. Rusting grasp used in this way instantaneously destroys 1d6 points of AC gained from metal armor (to the maximum amount of protection the armor offers) through corrosion.
Weapons in use by an opponent targeted by the spell are more difficult to grasp. You must succeed on a melee touch attack against the weapon. A metal weapon that is hit is destroyed. Striking at an opponent's weapon provokes an attack of opportunity. Also, you must touch the weapon and not the other way around.
Against a ferrous creature, rusting grasp instantaneously deals 3d6 points of damage + 1 per caster level (maximum +15) per successful attack. The spell lasts for 1 round per level, and you can make one melee touch attack per round.
PS:I don't think it makes sense for the sunder ability to even exist. I think it would make more sense if you could just target items if you want just by making an attack roll, but that is neither here nor there.
PS2:Scorching Ray would be good for attacking items if we could use ray attacks against them.
Orion you may redo your action.
Ok so changed action, DM has informed me that the saving throw roll I made can be kept. First Save would be a 20+25=45 Reflex.
(What is the damage for your spell?)
(Damage halved and marked down.)
Round 14
Init 10
Pinpointing the place where he detects Orion's movements he continues to touch down at the bottom of the pit and unleashes a full attack of Arrows at him from his Composite Longbow. The arrows glow with brilliant energy, flying right through any armor or shields mundane or magical to strike at Orion.
(Sadly those crit threats both missed due to concealment. What round were the rifts of ruins each cast in btw?)
(Just ignore the shooting you then.) Darius sinks to the bottom and makes himself prone while he waits for the rift spell to run dry.
Five magic missiles shoot down toward Darius, hitting him with a mildly forceful onslaught. On one side of the field, a rift closes with a violent shudder. Afterwords, the ferns of a forest floor return in that five foot stretch...as if nothing ever happened.
Round 15
Init 10
Darius does move much as the missiles strike, continuing the wait.
A feat.
More magical missiles shoot out, even as another pit closes.
Round 16
Init 10
Darius continues to lay prone.
Orion sends forth another barrage of missiles as a third of the six pits closes. Those who are above water would be able to hear some math, as Orion calculates the remain time on the last three pits (one of which Darius is in).
Orion, he can still see out of the rift, and make perception checks.
I am just making sure you did not make a stealth because you thought he could not perceive you.
(So auto failing on your stealth?)
Round 17
Init 10
Darius looks up to where he has determined his foe must be, smiling as Orion lets down his guard. He continued to wait for his chance, the pitiful missiles and pit mere scratches in this game that would be determined by the one who could outlast the others resources.
Another burst of magic missiles. No other rifts close, however.
Round 18
Init 10
Suddenly Darius springs into action surging up out of the pit with flight and making his way to the two strips of solid land where he lands on the ground his bow aimed at Orion.
(Note: I went back into the history to check something and discovered I made a slight mistake in my round number calculation. It should be round 19. I'll reflect this in my next post. Does this match up with your round tracking Orion? Greater invis would have been round 12 from my perspective.)
(Edit from last post: That just means now on your turn its round 20 of the battle so far.)
(No worries. Things should get faster as we each just hit each other with spell and weapons.)
Round 20
Tapping out the last of his high end magic, Darius loses track of Orion even as the sky above the arena is filled with clouds. The clouds look odd though, red lightning flashes between them and they seem malevolent. The pits seem to have vanished though.
(Btw I do appreciate the time stop in view, there is no way for me to stop it just helps track things.)
Round 20
Init 10
Darius suddenly finds the environment changed but his keen senses alert him to Orion's stealthy movement. He turns to track him if he is still in the sky and unleashes a full attack of arrows at him.
(All Attacks possess the brilliant Energy enhancement so ignore any armor or shield bonuses even if magically granted.)
A flushing of magic hits Darius, destroying his magical flight, followed by the pair of storm clouds leaping down, emitting sounds of thunder and lightning as they attempt to leave Darius prone...and weaponless.
Orion attempts to vanish in the thunder and bright bursts of lightning.
Orion moves within 15 feet of Darius, less than half his flying movement.
(After DM double checks all that for me here is my action to keep things moving.)
Round 21
Init 10
Darius lets out a laugh despite his current seemingly bad predicament. "Hiding behind your monsters scared little man? AS YOU SHOULD BE!" He casts defensively from his current position A powerful blast of fear, hitting both of the creatures.
(I will roll the Casting defensively if requested but with +30 vs dc 23 I don't think I can fail on a natural 1 based on what Watcher said earlier. DC would be 23.)
Both creatures are hit by a Fear spell(As would Orion if he were in the 30 foot cone but without a map unless the DM can calculate your position or your within 30 feet above me there is very little I can do to prove it would). Will saves please.
If both are panicked Darius will retrieve his bow while prone. Then on their turn both will take no actions but to flee from him at top speed which would probably be a flying run out of the arena for the next 17 rounds.
If one or both somehow make the save then he will draw his sword while still one the ground.
(Both Fail the DC and are Panicked for 17 rounds per the Fear spell.)
The storm clouds fly away, screaming like metal shearing. Darius appears to be doing nothing, however.
Round 22
Init 10
Darius stands up his bow in hand and notches another arrow listening and looking for any signs of the spell caster. Unfortunately he doesn't see anything so he holds his arrow ready for the opportunity.
(Would it be too much trouble to ask where each last location he pinpointed you was? It does make some difference since he can aim spells there if you don't move and range is a factor.)
Again, nothing seems to happen...
Round 23
Init 10
Darius continues to search for Orion waiting for him to slip up or his invisibility to fade. He also seems to be doing nothing.
(Perception impossible.)
A black ray shoots out from near the ground, hitting with full force against the anti-paladin. The person who shot the ray vanishes once again.
(Just waiting on DM for something that will affect next action.)
Round 24
Init Changed to 27
Readied action triggers in response to Orion attacking him with his reach spell. Init is changed to 1 before Orion's action.
Darius whirls suddenly and fires a single shot straight at Orion as the ray strikes him in the chest. The ray seem like a solid hit that would draw the life force from any man...yet Orion receives nothing(do not gain any HP or temp HPs from Vamp touch, spell has no effect). He just begins to laugh. "More! Come on surely you haven't run out of spells yet! I am at your mercy and yet you are so weak...after I have slain you I think I will track down your family and enjoy their screams while I torture them slowly for such a pitiful performance! I think for that one I'll slowly drain the life from your mother."
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Round 25
Init 27
Darius notches another arrow and waits for the sorcerer's next trick.
Orion your vampiric touch spell fails to give you any additional hit points.
Darius appears to do nothing once more, but he does throw up a spell you recognize, one Darius has thrown up multiple times on himself...Spell Turning. Orion then vanishes at that point.
Round 26
Init 27
Darius turns and fires more arrows at Orion, seeming to track him almost impossibly.
(Brilliant Energy Quality on all attacks)
A sphere of Force appears approximately 40 ft above Darius and those with good hearing can hear the chanting of a summoning spell.
(Emergency Force sphere must be Centered on you per the spell.)
What summoning spell?