The first direct measurement of a high resolution infrared absorption spectrum of an ionic complex, Ar-HN2+, is presented. The complex is generated in a continuous supersonic slit jet expansion with electron impact ionization. There have been observed 28 rotationally resolved transitions of the nu(1)+nu(s), combination band in the 2501-2510 cm(-1) region using a tunable diode laser. The band origin is determined at nu(0) = 2505.4998(4) cm(-1). (C) 1997 American Institute of Physics. [S0021-9606(97)04044-0].