A digitally controlled diode-laser spectrometer: Infrared spectrum of the ν4 band of acetonitrile between 890 and 960 cm -1
The ν4 vibration-rotation spectrum of acetonitrile (CH 3CN) has been measured using a newly constructed diode-laser spectrometer controlled digitally by a microprocessor. The spectrum was observed in the range between 890 and 960 cm -1 with Doppler-limited resolution. The P and R branches of the ν4 fundamental band have been assigned up to K = 9. A small anomaly found in the high K lines is being explained by an anharmonic resonance with the v8 = 3 3 state. The determined interaction constant is small, but significant.