Results of single vibronic level fluorescence measurements in aniline‐h7, aniline‐N, N‐d2, aniline‐d5, and aniline‐d7 are reported. For each excited level the radiative and nonradiative lifetimes and fluorescence yields have been obtained. The dependence of the nonradiative lifetime of the excited level on the excess energy in aniline‐h7 is seen to behave similarly to that in benzene for states independent of inversion mode excitation. Levels involving inversion amplitude must be treated separately; we interpret their lifetimes by postulating that a nonplanar triplet state is involved in the intersystem crossing. Deuteration in the ring and amino positions affects the nonradiative lifetimes to different degrees and leads to the rejection of crossing to the 3B2 state as the rate determining step. A detailed study of the dependence of the nonradiative process on excitation of the inversion mode was carried out using the methods of Heller, Freed, and Gelbart. The numerical calculations were based on Franck‐Condon overlap factors appropriate for transitions from a near planar initial state to a significantly bent final state. The experimental trends observed with excitation of inversion mode were qualitatively reproduced for all the molecules studied except aniline N, N‐d2.

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A comparison of the two spectra indicated that only two of the transitions used to prepare the optical states in aniline‐d5 have any overlap at all with aniline‐h7 transitions: I11 (a) overlaps the weak 6 a01−40 band in aniline‐h7, and 6 a01I11 (b) overlaps the somewhat stronger 101 transition in the h7 compound. It is tempting to use this overlap to explain the observed discrepancies in the lifetimes between the (a) and (b) pairs in aniline‐d5 (see Results section) since the I1 (a) and 6 a1I1 (b) levels have shorter lifetimes than the partner members. However, this argument is not consistent with the relative intensities of the overlapping transitions. This is very clear for the red member of 18 a01I11 at 35282 cm−1 in aniline‐d5, which occurs at the same energy as 101I11 in aniline‐h7. It can be seen from Fig. 4 that this latter band has approximately the same intensity as the 101 band in aniline‐h7, and is more intense than the 6 a01−40 band, and yet even were one to require all the intensity of the band at 35282 cm−1 to be ascribed to the 101I11 transition, applying that intensity to the I116a01 (b) band would still not explain the discrepancy in lifetimes in either pair of states in aniline‐d5. Of course, the major part of the intensity of the band in aniline‐d5 is due to the 18 a01I11 (a) transition as may be seen by comparison with the 18 a01I11 (b) partner which overlaps a very weak transition in aniline‐h7 and thus may be considered pure. It was therefore decided to use the available sample rather than going through the tedious process of isotope separation.
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For this calculation the HNH angle was taken to be 120 °, and the NH bond length 1.00 Å. The reduced mass for inversion mode motion was taken to be the moment of inertia of the NH2 fragment about an axis passing through its center of mass and parallel to the NH2 plane.
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