Collisional energy transfer in Na(4[ital p]--3[ital d])--He,H[sub 2] collisions

We have investigated the direct collisional energy transfer process Na*(4[ital p])+M[r arrow]Na*(3[ital d])+M, where M=He,H[sub 2] under gas cell conditions. We have measured the temporal profiles of the Na(3[ital d]--3[ital p]) sensitized fluorescence as a function of quenching gas pressure and fit the profiles to a two-state rate equation model to obtain the quenching rate coefficients from the Na*(4[ital p]) state. The total energy transfer rate coefficient out of the 4[ital p] state for He is small [(0.5[plus minus]0.2)[times]10[sup [minus]10] cm[sup 3]/s]. The total quenching rate coefficient out of the 4[ital p] state is much larger for H[sub 2][(3.9[plus minus]0.5)[times]10[sup [minus]10] cm[sup 3]/s]. Evidence suggests that the energy transfer rate coefficient for the 4[ital p]--3[ital d] process is [similar to]2.0[times]10[sup [minus]10] cm[sup 3]/s with the remainder of the 4[ital p] quenching being predominantly reactive. We also compare the far-red wing absorption line shapes for the NaHe and NaH[sub 2] systems.