Alabama is set to kill a man on death row using nitrogen gas on Thursday, employing the method for the second time ever after some witnesses described serious problems during the first nitrogen execution earlier this year.

Alan E. Miller, who was convicted in the 1999 murders of three men he believed were spreading rumors about him, is scheduled to be executed at 6 p.m. Central time in Atmore, Ala.

In January, the state carried out what was described as the first nitrogen execution anywhere in the world, and other states have said they are looking into doing so as well as they continue to experience problems obtaining lethal injection drugs.

Several witnesses to that execution said that the prisoner, Kenneth Smith, shook violently as the nitrogen gas was administered and then writhed before his body eventually stopped moving. Witnesses told The New York Times that the gurney had shaken in the execution chamber and that Mr. Smith had appeared to be gasping for air.

But the state’s attorney general, Steve Marshall, has hailed the execution, calling it “textbook” and saying that Alabama had become a pioneer that other states could follow. “Alabama has done it, and now so can you,” he said.

Nitrogen, a colorless, odorless gas, is not harmful in itself and makes up about 78 percent of the air. But when it is used in an execution, a prisoner is strapped to a gurney and a mask is placed over the head, after which a stream of pure nitrogen gas, absent life-sustaining oxygen, produces a fatal but supposedly painless form of suffocation known as nitrogen hypoxia. The method has been used in some medically assisted suicides.

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