A gas reservoir that receives a precursor has a gas-receiving unit which is arranged in a first receiving unit of a basic body and a sliding unit which is arranged movably in a second receiving unit of the basic body. The gas-receiving unit has a movable closure unit for opening or closing a gas outlet opening of the gas-receiving unit. In a first position of the sliding unit, a first opening of a sliding-unit line device is fluidically connected to a first basic body opening and a second opening of the sliding-unit line device is fluidically connected to a second basic body opening. In the second position of the sliding unit, the first opening is arranged at an inner wall of the second receiving unit and the second opening is arranged at the movable closure unit.