Pulsed quantum-cascade-laser (QCL) spectrometers are usually used to detect atmospheric gases with either the interpulse technique (short pulses, typically $5–20\mathrm{ns}$ ) or the intrapulse technique (long pulses, typically $500–800\mathrm{ns}$ ). Each of these techniques has many drawbacks, which we present. Particularly the gas absorption spectra are generally distorted. We demonstrate the possibility to use intermediate pulses (typically $50–100\mathrm{ns}$ ) for gas detection using pulsed QCL spectrometers. IR spectra of ammonia recorded in the $10\mu \mathrm{m}$ region are presented in various conditions of pulse emission. These experiences demonstrate the large influence of the pulse shape on the recorded spectrum and the importance to use our alternative method for gas detection with pulsed QCL spectrometers.