Spectrum MIR ATR spectrum of Na-exchanged montmorillonite (SWy-2) under 90% relative humidity of H2O vapor Spectrum MIR ATR spectrum of Na-exchanged montmorillonite (SWy-2) under 80% relative humidity of H2O vapor Spectrum MIR ATR spectrum of Na-exchanged montmorillonite (SWy-2) under 60% relative humidity of H2O vapor Spectrum MIR ATR spectrum of Na-exchanged montmorillonite (SWy-2) under 50% relative humidity of H2O vapor Spectrum MIR ATR spectrum of Na-exchanged montmorillonite (SWy-2) under 35% relative humidity of H2O vapor Spectrum MIR ATR spectrum of Na-exchanged montmorillonite (SWy-2) under 19% relative humidity of H2O vapor